EXPERIMENTAL 


ELECTROCHEMISTRY 


BY 


N.    MONROE    HOPKINS,    PH.D. 

Assistant  Professor  of  Chemistry  in  The  George  Washington  University ', 
Washington,  D.  C 


TOtb  ©ne  IbunDrcD  an£> 


UUu0tratfon0 


NEW  YORK 
D.    VAN    NOSTRAND    COMPANY 

23  MURRAY  AND  27  WARREN  STREETS 
1905 


Copyright,  1905, 

BY 
D.  VAN  NOSTRAND  COMPANY 


ROBERT  DRUMMOND,  PRINTER,   NEW  YORK 


DEDICATED  TO 

Cbarles  BDwarD  d&unroe 

AS   A   TOKEN   OF   ESTEEM 


A    4    I  O  Ft  I 


PREFACE. 


IT  has  been  the  aim  of  the  author  to  produce  a  book  that  will 
prove  useful  in  both  the  lecture  room  and  in  the  laboratory. 
Although  a  work  upon  the  subject  of  electrochemistry  must  pre- 
suppose a  working  knowledge  of  chemistry  and  electricity,  it  has  been 
the  object  of  the  writer  to  introduce  the  subject  as  clearly  as  possible, 
dealing  with  chemistry  and  electricity  without  assuming  too  much  on 
the  part  of  the  student.  The  book  is  so  written  that  it  may  be  read 
through  as  a  history  by  the  student,  presenting  theory  and  practice 
together,  with  the  introduction  of  an  ample  number  of  experiments 
to  supply  experimental  evidence  for  the  theories  advanced.  In  the 
later  and  more  practical  part  of  the  book,  exercises  in  preparing 
electrolytic  compounds  and  in  isolating  metals  are  introduced.  It 
has  also  been  the  aim  of  the  writer  to  introduce  new  material  with 
suggestions  for  additional  experiments  with  the  hope  that  the  work 
will  not  be  unwelcome  to  those  already  well  informed  in  the  subject. 
Electrochemistry  is  at  best  a  subject  for  the  advanced  student,  and 
in  order  to  carry  out  the  experimental  work  with  profit,  as  given 
here,  he  must  have  pursued  beforehand  laboratory  courses  in  both 
chemistry  and  physics.  If  the  more  mature  and  experienced  student 
profits  by  a  study  of  the  book,  or  the  instructor  obtains  assistance  in 
teaching  or  suggestions  for  new  work,  the  object  in  writing  the  book 
will  be  attained. 

N.  MONROE  HOPKINS. 

LABORATORIES  or  THE  GEORGE  WASHINGTON  UNIVERSITY, 
WASHINGTON,  D.  C. 


SOME  IMPORTANT  SUGGESTIONS  TO  STUDENTS  AND 
RESEARCH  WORKERS  IN  ELECTROCHEMISTRY. 


A  PERUSAL  of  the  works  devoted  to  electrochemistry,  especially 
the  earlier  ones,  will  show  as  a  rule  a  sad  and  almost  complete  lack 
of  important  data  relative  to  practical  manipulations.  This  absence 
of  governing  facts  in  the  note-books  of  many  students  and  research 
workers  also  renders  it  very  difficult  if  not  impossible  to  repeat  the 
work  with  any  certainty,  or  to  instruct  others  to  do  so.  The  author 
wishes  to  impress  upon  the  student  the  absolute  necessity  of  observing 
and  recording  numerous  electrical  factors  in  all  electrochemical 
work. 

Chemists,  until  very  lately,  have  shown  a  pathetic  need  of  elec- 
trical knowledge,  a  failing  only  rivalled,  it  may  be  said,  by  the  lack 
of  chemical  knowledge  exhibited  by  electricians.  It  should  be  con- 
stantly borne  in  mind  that  electrochemistry  is  primarily  the  work  of 
the  chemist.  The  application  of  the  electric  current  and  its  control, 
although  of  vital  importance,  is  subordinate  to  the  purely  chemical 
side.  Electrochemical  operations  are  essentially  chemical  and  based 
upon  purely  chemical  changes,  and  it  is  only  the  man  with  a  broad 
and  keen  insight  into  theoretical  chemistry  who  can  ever  hope 
to  make  a  successful  electrochemist  or  electrochemical  engineer. 
Nevertheless  a  thorough  working  knowledge  of  electricity  is  to-day 
absolutely  necessary  for  success.  Electrochemical  science  is  only 
to  be  mastered  by  the  man  with  a  chemical  and  physical  equipment. 

A  few  words  of  caution  relative  to  practical  work.  Do  not  begin 
an  experiment  or  a  preparation  by  roughly  mixing  up  an  electrolyte 
and  subjecting  it  to  the  action  of  an  unmeasured  electric  current 
in  a  haphazard  manner.  If  you  enter  in  your  note-books  that  a 
solution  of  a  certain  strength  was  electrolyzed  for  a  certain  time  by 

vii 


viii     SUGGESTIONS  TO   STUDENTS   AND   RESEARCH  WORKERS. 

a  current  of  so  many  amperes,  do  not  feel  that  you  have  recorded 
all  the  important  data.  You  have  not  begun  to  take  into  account 
the  necessary  governing  conditions.  What  of  the  temperature? 
What  of  the  electrode  area  and  current  density,  as  well  as  the  mate- 
rial of  the  electrodes  ?  What  was  the  electrode  tension  ?  The  specific 
gravity  before  and  after  electrolysis?  What  was  the  character  of 
the  apparatus  and  the  dimensions  of  the  cell  ?  Were  anode  and 
cathode  temperatures  the  same  or  was  there  a  difference  ?  These 
are  but  a  few  questions  that  could  be  asked  after  an  experimental 
run,  all  of  which  throw  important  light  upon  what  was  going  on. 
Let  the  student  have  constantly  in  mind  that  he  is  above  all  things 
a  chemist  and  doing  a  chemist's  work,  and,  secondly,  that  he  is  a 
physicist  or  electrician,  and  that  the  electric  current  which  he  is 
using  is  capable  of  application  in  numerous  ways.  An  electric 
current  is  composed  of  factors,  and  its  deportment  as  a  reagent  is 
largely  dependent  upon  these  factors.  A  student  who  mixes  up  a 
solution  in  a  hurry,  sticks  in  electrodes  more  or  less  clean,  and  turns 
on  the  current  will  never  get  the  most  out  of  a  possibility  except 
by  a  remote  chance;  and  if  he  is  a  careless  worker,  he  is  not  likely 
to  recognize  the  full  significance  of  a  success  if  by  chance  he  should 
succeed.  Some  cases  of  electrolysis  are  extremely  complicated,  and 
it  will  even  prove  necessary  at  times  to  repeat  the  same  experiment 
many  times  in  order  to  obtain  and  record  all  the  facts.  One  run 
may  be  made  for  anode  and  cathode  temperature  changes,  another 
for  density  changes,  and  another  for  analytical  purposes,  all  with  a 
constant  and  set  current  strength,  perhaps.  Do  not  feel  that  one 
must  use  large  quantities.  The  best  work  is  often  done,  by  repeated 
experiment,  using  small  quantities  of  material. 


TABLE  OF  CONTENTS. 


CHAPTER  I 

PAGE 

HISTORICAL  NOTES  AND  IMPORTANT  CLASSIC  RESEARCHES i 

Early  Experiment  of  Sir  Humphry  Davy  in  isolating  the  metals 
Sodium  and  Potassium.  Mechanism  of  electrolysis  of  potassium 
hydroxide  theoretically  considered.  Experimental  electrolysis  of  a 
solution  of  sodium  or  potassium  hydroxide.  The  theory  of  electroly- 
tic dissociation.  Practical  directions  for  the  application  and  control  of 
the  electric  current  in  experimental  work. 

CHAPTER  II. 

THE  THEORY  OF  ELECTROLYTIC  DISSOCIATION 17 

Electrolytes  and  non-electrolytes.  Simple  experiment  to  show  elec- 
trolytes and  non -electrolytes.  Laws  of  Boyle,  Gay-Lussac,  and  Avoga- 
dro  relative  to  the  behavior  of  substances  in  solution.  Osmotic  Pressure 
and  method  of  measuring  it.  The  Principle  of  Soret.  Application  of 
data  as  experimental  evidence  in  favor  of  the  theory  of  electrolytic 
dissociation. 

CHAPTER  III. 

THE  THEORY  OF  ELECTROLYTIC  DISSOCIATION  (continued) 32 

Additional  experimental  evidence  in  its  support.  The  lowering  of  the 
freezing-point  of  solvents.  The  elevation  of  the  boiling-points  of  solvents. 
The  neutralization  of  acids  and  bases.  The  dissociation  of  ammonium 
chloride.  Dissociating  action  of  water  and  other  bodies.  Practical 
experiment  to  show  dissociation  by  increase  in  molecular  conductivity 
and  color  change.  Summary  of  experimental  facts  in  support  of  the 
theory  of  electrolytic  dissociation. 

CHAPTER  IV. 

NOVEL  EXPERIMENTS  IN  "ELECTROLYTIC  INDUCTION." 50 

Ostwald's  experiment  in  static  induction  to  show  the  presence  of 
"free  ions."  Ostwald  and  Nernst's  experiment  in  static  induction  to 

ix 


TABLE   OF  CONTENTS- 

PAGE 

show  the  presence  of  free  ions.  Author's  experiment  in  static  induction 
to  show  the  presence  of  free  ions  through  the  agency  of  the  reflecting 
galvanometer  as  a  chemical  indicator.  Experiments  to  show  effect  of 
magnetism  upon  a  coil  of  electrolyte.  Experiment  to  show  the  effect 
of  an  electric  current  traversing  an  electrolyte  upon  a  magnetic  needle. 
Experiment  to  show  and  to  measure  the  effect  of  an  electric  current 
traversing  an  electrolyte,  upon  a  mass  of  iron.  Comparisons  between 
magnetic  effects  of  conductors  of  first  and  second  class  when  carrying 
current.  Experiment  to  show  electrodeless  conduction.  Experiment 
to  show  and  to  study  the  effect  of  alternating  currents  upon  electrolytes. 
The  influence  of  "  frequency, "  the  energy  factor  remaining  constant. 

CHAPTER  V. 

VELOCITY  OF  ELECTROLYTIC  CONDUCTION." 66 

Ostwald's  experiment  to  show  instantaneous  conduction  through 
electrolytes.  Experiments  with  a  high-speed  special  band  chronograph 
capable  of  dividing  a  second  into  a  million  parts.  Author's  experiment 
to  show  instantaneous  conduction  through  electrolytes,  and  to  compare 
the  time  required  for  conduction  between  conductors  of  the  first  and  second 
class.  Lodge's  experiment  for  determining  the  absolute  velocities  of 
the  ions.  The  significance  of  the  data  in  hand  in  relation  to  the  theory 
of  electrolytic  dissociation. 

CHAPTER  VI. 

FARADAY'S  LAW 80 

Electrochemical  and  chemical  equivalents.  Experimental  demon- 
stration of  Faraday's  Law.  Table  of  a  few  electrochemical  equivalents 
arranged  as  a  guide  for  the  student.  Validity  of  Faraday's  Law.  Law 
of  Dulong  and  Petit  in  relation  to  the  facts  brought  out  by  Faraday's 
Law.  Short  table  of  atomic  heats.  The  construction  and  use  of  the 
silver  voltameter.  The  copper  voltameter.  The  gas  voltameter. 
Distinction  between  current  required  to  electrolyse,  and  the  energy 
absorbed.  Experiment  to  show  the  energy  absorbed  in  different 
electrolytes  when  a  common  current  is  passing.  Experiments  to  show 
the  mechanical  transport  of  ponderable  material.  The  experimental 
electrolysis  of  zinc  chloride.  The  electrolysis  of  solid  glass  when  sub- 
jected to  heat.  Experiments  with  frozen  electrolytes.  Experiment  to 
show  heat  convection  in  electrolysis. 

CHAPTER  VII. 

ENERGY  REQUIRED  IN  ELECTROLYSIS 100 

Practical  formula  for  calculating  it.  Partial  table  of  the  heats  of 
formation  of  chemical  compounds.  The  experimental  liberation  of 


TABLE   OF   CONTENTS.  XI 


metallic  magnesium  from  an  igneous  or  fused  electrolyte,  with  current 
and  energy  determinations.  The  electrolysis  of  concentrated  sulphuric 
acid  into  its  elements,  with  energy,  calculation  and  theoretical  mechanism 
of  electrolysis.  The  separation  of  metals  through  adjustment  of 
electrode  tension.  The  construction  and  operation  of  a  rotating  anode 
equipment  for  the  rapid  electro-deposition  of  metals.  Experiment  with 
copper  sulphate  solution  to  show  concentration  changes.  Theory  upon 
which  the  concentrations  are  believed  to  take  place. .  Experimental 
apparatus  of  Mather  and  Jones  for  determining  concentration  changes 
and  calculating  the  relative  velocities  of  the  ions. 

CHAPTER  VIII. 

IMPORTANT  CONDITIONS  TO  BE  NOTED  IN  ELECTROCHEMICAL  OPERATIONS.  117 

A  table  showing  useful  tabulation  of  data.  The  influence  of  current 
density  on  oxidation  and  reduction.  Experiment  to  show  the  effect  of 
current  density  upon  oxidation  and  reduction.  Experimental  arrange- 
ment of  Beckmann  thermometers  for  studying  electrode  temperatures 
in  electrochemical  research.  The  electrolytic  production  of  caustic 
soda  and  chlorine  from  salt.  The  electrolytic  production  of  white  lead 
from  lead  electrodes.  The  electrolytic  production  of  cadmium  yellow. 
The  electrolytic  production  of  mercury  vermilion.  The  electrolytic 
production  of  Scheele's  Green.  The  electrolytic  production  of  Berlin 
Blue.  Apparatus  and  equipment. 


CHAPTER  IX. 

THE  ELECTROLYTIC  PREPARATION  OF  POTASSIUM  CHLORATE  FROM  POTAS- 
SIUM CHLORIDE 133 

The  electrolytic  preparation  of  sulphur  trioxide.  Introduction  of 
special  apparatus  for  the  electrolysis  of  solutions  yielding  gaseous  prod- 
ucts and  means  for  condensing  and  estimating  same.  The  electrical 
production  of  Ozone.  Brief  history  of  ozone  and  its  applications. 
Ozone  generators  using  sulphuric  acid.  Ozone  generators  using 
metal-coated  tubes.  The  commercial  production  of  ozone  and  the 
purification  of  drinking  water  through  its  use. 

CHAPTER  X. 

THE  PRODUCTION  OF  NITRIC  ACID  FROM  THE  ATMOSPHERE 150 

Brief  history  of  nitric  acid  and  the  historic  chemical  and  electrical 
means  of  obtaining  it  from  air.  Various  forms  of  combustion  chambers 
for  the  treatment  of  the  air  or  gases  drawn  in.  Influence  of  the  size  of 


TABLE   OF   CONTENTS. 


combustion  chambers.  Influence  of  amperage  and  energy  in  secondary 
of  transformers,  or  in  the  flaming  arcs  used.  Influence  of  temperature. 
The  experimental  and  commercial  pieces  of  apparatus  designed  and  in 
use.  The  construction  of  a  simple  rotating  electrode  equipment  for  the 
production  of  nitric  acid  from  air  in  the  lecture-room  or  laboratory. 

CHAPTER  XI. 

THE  ISOLATION  OF  THE  METALS  SODIUM  AND  POTASSIUM 165 

Brief  historic  sketch  of  the  early  work.     Processes  of  extraction. 
Method  of  Sir  Humphry  Davy.    Apparatus  of  Charles  Watt.     Borscher's 
sodium  cell,  and  tabulation  of  workable  conditions.     Castner  cell  and     . 
process.     The  design  of  a  small  Castner  cell  for  isolating  sodium  and 
potassium  on  a  small  scale.     Calculation  for  minimum  voltage  necessary 

for  isolating  sodium. 

\ 

CHAPTER  XII. 

THE  ISOLATION  OF  THE  METAL  ALUMINUM 174 

Brief  history  and  outline  of  researches  upon  the  production  of 
aluminum.  Carbon  reduction  furnaces.  Borscher's  furnace.  De- 
ville's  apparatus.  Hall's  furnace.  Heroult's  furnace.  The  pro- 
duction of  aluminum  bronze.  Method  of  charging  and  operating 
furnaces  for  the  isolation  of  the  metal  and  the  production  of  aluminum 
bronze. 

CHAPTER  XIII. 

THE  ISOLATION  OF  CALCIUM 186 

Outline  of  the  early  work  in  isolating  this  metal,  enumerating  the 
difficulties  encountered.  Bunsen's  directions  and  reference  to  the 
importance  of  current-density  conditions.  Illustration  in  section  and 
detail  of  an  experimental  calcium  furnace,  with  instructions  for  preparing 
the  metal  upon  a  small  scale.  Difficulties  met  and  precautions  necessary. 
Borscher's  experimental  calcium  furnace  and  method  of  operating  it. 


CHAPTER  XIV. 

THE  ELECTRIC  FURNACE  AND  FURNACE  PRODUCTS 194 

The  construction  of  a  wire-resister  muffle-furnace  for  temperatures 
under  1600°  C.  Vertical  type  upon  same  principle,  with  directions  for 
making.  Author's  " Series  Carbon"  furnace  for  the  production  of  high 
temperatures  on  the  no-volt  circuit.  Illustration  of  furnace,  diagram 


TABLE   OF   CONTENTS.  xlii 

PAGB 

of  connections,  and  method  of  using.  Directions  for  the  production 
of  calcium  carbide  upon  an  experimental  scale.  The  construction  of 
an  arc  or  resister  furnace  for  the  production  of  the  highest  temperatures 
when  ample  current  is  available. 


CHAPTER  XV. 

PREPARATION  OF  ORGANIC  COMPOUNDS 207 

The  electrolysis  of  sodium  acetate  with  the  liberation  of  hydrogen  and 
ethane.  The  electrolytic  production  of  iodoform.  Detailed  directions 
for  producing  small  quantities  in  the  laboratory.  The  synthesis  of 
acetylene.  The  production  of  carbon  disulphide  and  outline  of  com- 
mercial preparation.  The  production  of  chloroform.  Electrolytic 
oxidation.  The  preparation  of  kanarin.  Apparatus  of  Hoffman. 
Electrolytic  reduction. 


CHAPTER  XVI. 

THE  PRIMARY  CELL 219 

Historic  outline  of  early  theories  to  account  for  the  origin  of  the 
current.  The  production  and  origin  of  current  in  the  light  of  modern 
physical  chemistry.  The  phenomenon  of  solution  tension.  Experiment 
to  show  "  chemical  action  at  a  distance. "  The  theory  of  the  cell  and  the 
theory  of  electrolytic  dissociation.  Nernst  and  Helmholtz's  "double 
layer."  The  normal  electrode  and  its  uses.  Neuman's  table  of  potential 
differences  between  metals  and  their  salts.  The  tension  series  of  the 
metals.  The  chemistry  and  electrochemistry  of  the  Daniell  cell. 
Calculation  of  electromotive  force  in  primary  batteries. 


•CHAPTER  XVII. 

THE  SECONDARY  CELL 237 

Conditions  to  be  studied  in  the  secondary  cell.  The  construction 
and  study  of  a  simple  experimental  cell.  Typical  discharge  curve  of 
ideal  storage-battery.  Author's  reflecting  hydrometer  for  studying 
density  changes  in  batteries.  Sellon's  hydrometer.  The  theory  and 
chemistry  of  the  storage- battery.  Difficulties  in  the  way  of  a  clear  and 
perfect  study.  Ayrton's  theory  of  the  secondary  cell.  Theory  of 
Plante.  Views  of  Treadwell.  The  charging  and  care  of  storage-bat- 
teries. Rules  for  the  maintenance  of  cells.  Calculation  of  capacity  of 
storage-cells.  Calculation  of  electromotive  force. 


xiv  TABLE.  OF  CONTENTS 


CHAPTER  XVIII. 

PAGE 

ELECTRICITY  FROM  CARBON 250 

Primary  and  secondary  powers.  Zinc  as  fuel.  Thermoelectricity. 
Thermoelectric  battery  and  couples.  Warning  to  student  in  research 
work  not  to  confound  thermoelectric  phenomena.  BecquereFs  experi- 
ment on  the  oxidation  of  carbon  to  produce  the  electric  current  direct. 
Work  of  Jablochkoff  and  Jacques.  Ostwald's  outline  of  necessary  con- 
ditions for  success.  Solution  and  ionization  of  carbon.  Experiment 
to  show  solution  of  carbon.  Lack  of  data  in  most  cases  where  research 
work  has  been  done.  Edison's  furnace  wrong  in  principle  for  the 
oxidation  of  carbon  to  electricity.  Outlook  for  the  solution  of  the 
problem. 

CHAPTER  XIX. 

USEFUL  PIECES  OF  APPARATUS 259 

Conductivity  cells  for  studying  electrolytes  with  movable  and 
stationary  electrodes.  Delicate  electrolytic  rheostat.  Electrolytic  test- 
tubes.  Electrolytic  test-tube  with  removable  porous  partition.  Hoff- 
mann's apparatus.  Directions  for  making  one  upon  a  large  scale.  The 
Wenhelt  interrupter  and  its  application  to  induction-coils  and  apparatus 
requiring  an  intermittent  current.  The  aluminum  rectifier  for  convert- 
ing alternating  currents  into  direct  currents.  Principle  upon  which 
the  aluminum  rectifier  is  believed  to  act. 


CHAPTER  XX. 

BIBLIOGRAPHY  CHRONOGRAPHICALLY  ARRANGED 267 

A  review  of  the  historic  writings  upon  electrolysis  and  electrochem 
istry,  electrometallurgy,  etc.,  to  date.  The  bibliography  is  not  claimed 
to  be  in  anywise  complete,  but  it  is  thought  to  cover  many  classic  writings 
as  well  as  numerous  important  researches  of  a  more  recent  and  practical 
nature.  The  bibliography  as  introduced  should  be  of  especial  value 
to  students  interested  in  early  work. 


EXPERIMENTAL   ELECTROCHEMISTRY. 


CHAPTER   I. 

HISTORICAL  NOTES,  AND  IMPORTANT  CLASSIC  RESEARCHES, 
WITH  SIMPLE  DIAGRAMS  OF  THE  USE  OF  THE  ELEC- 
TRIC CURRENT  TO  ELECTROLYSIS. 

BELIEVING  that  the  proper  introduction  to  this  volume  should 
give  a  review  of  the  historical  work,  together  with  a  notice  of  the 
more  basic  experimental  evidence  obtained  in  support  of  the  theories 
and  laws  advanced,  the  opening  pages  are  devoted  to  recording  the 
more  important  researches  and  discoveries. 

As  this  chapter  deals  jointly  with  electricity  and  chemistry,  the 
best  place  to  commence  the  recording  of  events  is  the  time  when  the 
galvanic  or  voltaic  current  was  introduced  or  grafted  into  chemistry. 
The  history  of  electrochemistry  before  the  discovery  of  the  gal- 
vanic current  requires  but  a  brief  description.  Ages  before  the  dis- 
covery of  voltaic  electricity  it  had  been  observed  that  various  metals, 
by  being  simply  immersed  in  metallic  solutions,  became  coated  with 
the  metal  previously  dissolved  in  the  liquid. 

Thousands  of  years  ago  Zosimus  mentioned  the  deposition  of 
bright  metallic  copper  upon  iron  immersed  in  a  solution  of  a  copper 
salt.  In  the  year  1752  Sulzer  remarked:  "If  you  join  two  pieces  of 
lead  and  silver,  so  that  they  will  be  in  the  same  plane,  and  then  lay 
them  upon  the  tongue,  you  will  notice  a  certain  taste  resembling 
that  of  green  vitriol,  while  each  piece  apart  produces  no  such  sensa- 
tion." Becaria  demonstrated  in  1772  that  metallic  zinc  could  be 
obtained  from  its  oxide  by  means  of  a  powerful  electric  spark,  as 
from  a  battery  of  Leyden  jars.  Paetz  and  Van  Troostvik  in  1790 


2  EXPERIMENTAL  ELECTROCHEMISTRY. 

decomposed  water  by  passing  electric  sparks  through  it  by  means 
of  very  fine  gold  wires. 

Up  to  the  close  of  the  eighteenth  century,  however,  a  possible 
affiliation  of  electricity  with  chemistry  was  not  thought  of,  the  second 
celebrated  experiment  of  Galvani  upon  the  nerves  and  limbs  of 
recently  killed  frogs,  in  1786,  marking  the  dawn  of  what  is  now 
known  as  dynamic  electricity.  As  early  as  1780  it  was  observed 
by  Galvani  that  the  limbs  of  dead  frogs  contracted  violently  when 
hung  upon  a  copper  hook  in  the  neighborhood  of  a  frictional  elec- 
trical machine,  at  each  disruptive  discharge  of  the  then  known  and 
so-called  static  electricity.  Six  years  later  Galvani  obtained  the 
same  results  with  the  limbs  and  nerves  of  frogs  without  the  agency  of 
an  electrical  machine,  simply  by  bringing  a  copper  wire  joined  to  a 
nerve  and  one  of  the  limbs  in  contact  with  a  piece  of  iron.  The 
analogy  of  these  results,  although  six  years  separated,  caused  Galvani 
to  refer  the  phenomenon  to  a  common  agency,  namely,  electricity. 
Galvani  describes  his  discovery  of  what  he  called  "animal  electricity" 
in  his.  famous  "De  Viribus  Electricitatis "  of  1791  in  the  following 
words:  "It  is  principally  found  in  the  nerves  and  muscles,  and  its 
path  seems  to  be  from  the  muscles  to  the  nerves,  or  rather  from  the 
nerves  to  the  muscles  by  the  shortest  route,  as  in  the  Leyden  jar. 
There  is  in  every  part  a  double  electricity,  positive  and  negative,  and 
disjunctive.  One  exists  internally  in  the  muscles,  the  other  externally ; 
so  that  the  muscular  fiber  acts^ike  a  little  Leyden  jar,  and  the  nerves 
simply  serve  the  office  of  conductors."  In  the  year  1792  Alexander 
Volta  discarded  the  theory  given  by  Galvani;  and  from  the  fact  that 
convulsions  took  place  more  energetically  when  there  were  dissimilar 
metals  in  the  connecting  circuit,  instead  of  only  one  variety,  attributed 
the  electricity  to  their  being  unlike,  and  laid  the  basis  for  the 
contact  theory  of  electricity.  In  1792  Prof.  Fabroni,  of  Florence, 
first  suggested  chemical  action.  The  following  words  are  from 
Prof.  Fabroni's  report  to  the  Scientific  Academy  of  Florence,  con- 
cerning experiments  which  he  had  made  with  metals  which  he  had 
immersed  in  water.  He  said  that  he  was  convinced  that  "a  chemical 
action  had  taken  place,  and  that  it  was  unnecessary  to  seek  else- 
where the  nature  of  the  new  stimulus,  that  it  was  manifestly  owing 
to  the  slow  combustion  and  oxidation  of  the  metal ;  which  combustion 
must  have  been  accompanied  by  an  attraction  of  oxygen  and  by  a 


HISTORICAL  NOTES   AND   CLASSIC   RESEARCHES.  3 

disengagement  of  light  and  caloric."  In  1793  Alexander  Volta  of 
Pavia  advanced  his  contact  theory  of  electricity  in  the  Philosophical 
and  Medical  Journal  of  Leipsic,  and  later,  in  his  famous  memoir 
to  the  French  National  Institute,  he  gives  an  exposition  of  his- 
"electromotive  apparatus."  It  is  made,  he  says,  writing  in  1801 
in  the  above  celebrated  communication  to  the  National  Institute, 
"in  the  form  of  a  pile  or  of  a  range  of  cups,  and  consists  in  the 
simple  metallic  pairs  of  plates,  so  arranged  as  to  impel  the  electric 
fluid  in  one  particular  direction.  The  zinc  is  laid  upon  the  silver, 
the  moist  pasteboard  over  the  zinc,  and  so  on  consecutively."  He 
called  the  different  conducting  substances  the  "motors,"  and  their 
arrangement  a  "circle,"  "in  which  an  electric  stream  is  occasioned,, 
which  ceases  only  when  the  circle  is  broken,  and  which  is  renewed 
when  the  circle  is  again  rendered  complete."  The  power  of  chemical 
decomposition  of  the  voltaic  "  stream "  or  current  was  immediately 
noticed  by  numerous  workers,  Nicholson  and  Carlisle  being  the  first  to 
decompose  water  by  means  of  such  a  current  of  electricity  on  May  2, 
1800,  and  soon  afterward  Dr.  Henry  of  Manchester  decomposed  nitric 
and  sulphuric  acid,  and  also  ammonia,  by  similar  means.  With  the 
discovery  of  the  voltaic  current  scientists  became  occupied  with  two 
great  questions:  First,  what  is  the  true  principle  of  the  voltaic  cell 
and  the  source  of  the  electricity  ?  And  second,  what  is  the  mechan- 
ism of  electrolysis,  or  in  other  words,  how  does  the  electric  current 
decompose  chemical  compounds?  Let  us  take  up  the  question  of 
electro-decomposition  first  in  the  present  chapter,  and  discuss  the 
origin  of  the  electric  current  when  we  are  in  a  better  position  to 
appreciate  the  various  factors. 

In  1801  Dr.  Wollaston  discovered  that  if  a  piece  of  silver  in 
connection  with  a  more  positive  metal  be  put  into  a  solution  of  cop- 
per, the  silver  becomes  coated  with  copper,  which  coating  will  stand 
the  operation  of  burnishing.  During  the  same  year  Gerboin  first 
noticed  the  movement  produced  in  mercury  during  the  act  of  electroly- 
sis. 

In  1803  Kissinger  and  Berzelius  discovered  that  by  means  of  a 
voltaic  current  the  elements  of  water  and  of  neutral  salts  were  trans- 
formed to  the  respective  polar  wires  immersed  in  the  liquid;  and 
Cruickshank,  about  the  same  time,  observed  the  electro-deposition 
of  lead,  copper,  and  silver  upon  one  of  the  polar  wires  (the  one  con- 


4  EXPERIMENTAL  ELECTROCHEMISTRY. 

nected  with  the  zinc  end  of  the  battery)  immersed  in  solutions  of 
salts  of  those  metals,  and  was  thus  led  to  suggest  the  analysis  of 
minerals  by  means  of  the  voltaic  current. 

In  1805  Brugnatelli  observed  the  electro-deposition  of  gold  upon 
silver  when  the  former  was  made  the  negative  pole  in  a  solution  of 
"ammoniuret  of  gold";  he  also  discovered  the  electro-deposition 
of  zinc. 

The  most  brilliant  and  striking  proof,  however,  of  the  great 
breaking-down  power  of  the  electric  current  when  applied  to  chemical 


FIG.  i. — Reproduction  of  Sir  Humphry  Davy's  Classic  Experiment  in  Isolating  the 
Metals  Sodium  and  Potassium. 

substances  was  discovered  on  October  6,  1807,  by  Sir  Humphry 
Davy  in  the  electrolytic  decomposition  of  potash  and  soda,  and  the 
liberation  of  their  respective  metals,  by  a  current  from  a  voltaic 
battery  of  274  cells. 

Let  us  study  this  classic  experiment,  and  begin  our  practical 
laboratory  work  by  reproducing  it,  and,  under  the  stimulus  of  the 
famous  experiment,  undertake  to  explain  the  mechanism  of  electroly- 
sis, or  in  other  words,  to  learn  if  possible  what  takes  place  when  an 
electric  current  is  made  to  pass  through  the  substances  Davy  used. 
First  let  us  look  into  the  actual  arrangement  of  the  details  of  the 


HISTORICAL  NOTES  AND    CLASSIC   RESEARCHES. 


5 


experiment.  For  this  purpose  we  will  turn  to  our  illustration.  In 
our  electrochemical  studies  a  fair  knowledge  of  chemistry  is  pre- 
supposed, although  the  author  will  deal  with  the  subject  through- 
out as  simply  and  as  clearly  as  possible.  A  small  cavity  was  made  in 
a  piece  of  caustic  soda,  or  sodium  hydroxide  (NaOH),  which  was 
then  moistened  with  water.  This  was  placed  upon  a  piece  of  sheet 
platinum  connected  with  the  positive  wire  of  a  voltaic  battery. 
Mercury  was  poured  into  the  cavity  and  connected  with  the  negative 
wire  of  the  battery,  thus  closing  the  circuit  through  the  system. 


FIG.  2. — 5,  Block  of  Moistened  Caustic  Soda  or  Potash.  M,  mercury  in  cavity  of 
caustic  soda  or  potash;  P,  platinum  wire  dipping  into  mercury;  Pr,  platinum 
sheet  for  positive-wire  connections. 

Electrolysis  began  immediately,  the  metal  sodium,  from  the  sodium 
hydroxide,  being  liberated  from  the  hydroxyl  and  propelled  to  the 
mercury,  with  which  it  amalgamated.  After  about  an  hour,  having 
kept  the  caustic  soda  moistened  by  the  addition  of  water  from  time 
to  time,  the  mobile  mercury  became  quite  stiff,  due  to  the  presence 
of  the  sodium  amalgamated  with  it.  This  experiment  can  be  most 
easily  reproduced,  and  the  sodium  be  freed  from  the  mercury  by 
distillation  of  the  mercury,  leaving  the  sodium  behind,  or  the  amalgam 
may  be  put  into  water,  when  the  sodium  will  react  with  the  water 
(2Na  +  2H2O  =  2NaOH+H2),  setting  hydrogen  free,  which  may  be 
ignited,  and  forming  a  solution  of  sodium  hydroxide,  which  may  be 
obtained  in  the  solid  form  by  evaporating  to  dryness  on  a  watch-glass. 
In  distilling  the  mercury  from  the  sodium,  the  reader  is  referred  to 
any  general  work  on  chemistry,  where  the  proper  precautions  are 


6  EXPERIMENTAL  ELECTROCHEMISTRY. 

given  for  this  operation.  This  is  a  beautiful  experiment,  and  it  is 
strongly  urged  that  every  student  in  electrochemistry  repeat  it  for 
himself.  In  the  place  of  the  historic  battery  of  274  cells,  six  or  eight 
modern  cells  of  battery  will  suffice,  although  the  direct  current  from 
a  lighting  system,  properly  modified  by  lamps,  is  to  be  desired. 
The  use  of  lighting  circuits  and  lamps  for  electrochemical  processes 
will  be  fully  dealt  with  later.  Let  us  now  look  into  the  theory  of 
the  breaking  up  of  the  sodiurn  hydroxide  by  the  electric  current. 
Davy  might  have  used  a  strong  solution  of  sodium  hydroxide  in 
water  placed  in  a  dish,  with  a  layer  of  mercury  at  the  bottom  to  act 
.as  the  negative  electrode,  and  to  receive  the  sodium,  and  the  principle 
would  have  been  just  the  same.  Let  us  represent  graphically  such 
a  solution,  and  illustrate  by  diagram  the  various  steps  in  the  electroly- 
sis. As  an  exposition  of  all  the  ancient  theories  would  lead  to  con- 
fusion in  our  practical  work,  the  latest  views  only  upon  this  subject 
are  given,  and  we  will  base  our  work  upon  the  famous  theory  of 
"  electrolytic  dissociation."  This  theory  explains  in  a  most  satis- 
factory manner  many  chemical  and  electrochemical  phenomena, 
which  without  its  aid  would  be  hopeless.  This  celebrated  doctrine 
was  advanced  by  Svante  Arrhenius  in  1887,  and  although  there  are 
many  chemists,  physicists,  and  physical  chemists  who  do  not  accept 
it,  they  have  not  advanced  anything  better  to  account  for  the  numerous 
things  it  explains.  There  is  the  most  excellent  experimental  evi- 
dence in  support  of  this  doctrine,  which  will  be  taken  up  in  detail 
later  on.  For  the  present  we  will  assume  it  to  be  true,  for  besides 
t>eing  a  theory  of  exceptional  beauty,  it  will  be  of  great  assistance 
to  us  in  all  our  work  in  electrochemistry.  The  theory  simply  states 
that  the  molecules  of  certain  chemical  substances,  when  dissolved  in 
water,  break  up  into  ultimate  parts,  and  that  these  ultimate  parts 
carry  upon  them  small  charges  of  electricity.  Let  us  look  at  the 
matter  from  a  diagrammatic  point  of  view.  The  accompanying 
illustration  (Fig.  3)  shows  a  series  of  vessels  in  which  we  will  electro- 
lyze  a  solution  of  potassium  hydroxide.  A  represents  two  molecules 
of  potassium  hydroxide  about  to  be  plunged  into  the  vessel  of  water. 
Here  the  familiar  molecular  chemical  formula  of  the  base  is  given. 
B  shows  what  is  supposed  to  take  place  according  to  the  theory  of 
electrolytic  dissociation.  The  potassium  atom  breaks  away  from  the 
liydroxyl  group,  and  takes  upon  itself  a  charge  of  positive  electricity, 


HISTORICAL  NOTES   AND  CLASSIC   RESEARCHES. 


B 


K 

OH 

K 

OH 

K 
K 

OH 
0~H 

and  the  hydroxyl  group  takes  upon  itself  a  charge  of  negative  electric- 
ity. All  this  is  believed  to  happen 
simply  upon  dissolving  in  the  water,  with 
no  electrical  influence  whatever  being 
brought  to  bear.  Here  we  have,  accord- 
ing to  our  theory,  free  potassium  de- 
tached, and  isolated  from  the  hydroxyl 
radical,  floating  around  independently 
in  the  water,  but  covered  with  a  charge 
of  electricity.  At  first  sight  of  such  a 
diagram  the  majority  of  chemical  readers 
would  say  that  they  did  not  believe  a 
word  of  it,  for  in  the  first  place  we  could 
not  have  free  potassium  floating  about 
in  water  without  a  violent  reaction  taking 
place  between  it  and  the  water;  and  in 
the  second  place,  where  did  the  charge 
of  electricity  come  from?  Let  us  not 
attempt  to  answer  these  questions  for 
the  present,  but  accept  the  truth  of  the 
theory  for  the  time  being,  and  take  up 
the  next  step  in  the  electrolysis.  In  C 
we  have  introduced  into  the  vessel  two 
electrodes,  one  positive  and  the  other 
negative,  as  they  are  connected  to  the 
positive  and  negative  ends  of  a  voltaic 
battery  respectively.  We  know  from  our 


FIG.  3. — A,  two  molecules 
of  potassium  hydroxide  before 
immersion  in  water;  B,  the 


elementary  physics  and    electricity  that 

J    r    J  J  same   molecules    broken   down 

charges  of  like  signs  repel,  and  those  of  into  "ions"  on  being  dissolved; 
unlike  signs  attract.  In  this  case,  if  the  c>  the  "ions"  being  attracted 
ultimate  parts  of  the  molecule  of  po- 

• 


ions 

to  electrodes  of 
ity;    D,  "ions"  arrived  at  the 

tassmm    hydroxide    carry    positive    and    electrodes  ready  to  give  up  their 

negative   electrical  charges  respectively, 

there  should   be  an  attraction  between 

the    negative    charge    of    one    electrode 

and  the  positive  charge  of  the  potassium 

on    the   one   hand,    and    an    attraction 

between  the  positive  charge  of  the  other  electrode  and  the  negative 


charges;  E,  the  electrical  char- 
ges neutralized,  the  "ions"  be- 
come atoms  and  react  to  form 
potassium  hydroxide  again,  and 
water,  and  setting  free  oxygen 
and  hydrogen  gas. 


8  EXPERIMENTAL   ELECTROCHEMISTRY. 

charge  on  the  hydroxyl  group  on  the  other  hand.  If  all  this  is  true, 
there  will  be  a  movement  of  the  potassium  toward  the  negative 
electrode,  and  a  movement  in  the  other  direction  of  the  hydroxyl 
group  toward  the  positive  electrode,  as  indicated  by  the  small  arrows 
in  the  diagram.  These  ultimate  parts  of  molecules  are  called  "ions," 
whether  they  consist  of  a  single  atom,  like  our  potassium  with  its 
electrical  charge,  or  whether  they  consist  of  a  group  of  atoms,  like 
our  hydroxyl,  with  its  electrical  charge.  Let  us  then  adopt  the 
technical  term,  and  speak  of  the  potassium  hydroxide  molecule  as 
breaking  down,  in  the  presence  of  water,  into  a  positive  potassium 
ion  and  a  negative  hydroxyl  ion.  The  next  diagram,  D,  shows  the 
potassium  ions  arrived  at  the  negative  electrode  and,  the  hydroxyl 
ions  arrived  at  the  positive  electrode.  We  may  think  of  the  electrical 
charges  upon  these  ultimate  parts  of  the  molecule  as  having  a  pro- 
tective action,  that  is  to  say,  rendering  them  inert  so  far  as  the  water 
is  concerned.  We  know  that  we  could  not  put  ordinary  metallic 
potassium  into  water  without  a  violent  reaction  taking  place,  with 
the  liberation  of  hydrogen  and  the  formation  of  potassium  hydroxide. 
Now  let  us  account  for  the  passive  state  of  the  ion  potassium  in  the 
water  to  be  due  to  the  protective  action  of  the  electrical  charge. 
What  happens  when  this  ion  reaches  the  electrode  ?  We  have  plenty 
of  negative  electricity  there  with  which  to  neutralize  the  positive 
electricity  upon  the  potassium,  and  neutralization  quickly  takes 
place.  The  diagram  E  shows  the  next  step;  there  the  electrical 
charges  have  been  neutralized  and  removed,  and  instead  of  ions  we 
now  have  ordinary  chemical  atoms  and  groups  of  atoms.  In  the 
lower  left-hand  corner  of  this  last  diagram  two  molecules  of  water 
have  been  graphically  inserted;  for  as  soon  as  the  potassium  ions 
become  atoms,  we  know  as  general  chemists  that  there  will  be  a 
reaction  to  form  potassium  hydroxide,  with  the  liberation  of  hydrogen. 
The  water  was  not  represented  in  the  previous  diagrams  simply 
because  it  played  the  part  of  solvent  only,  and  did  not  combine 
chemically  with  our  ions.  The  arrows  here  indicate  the  setting 
free  of  two  atoms  of  hydrogen  at  the  negative  electrode,  and  the  forma- 
tion of  a  molecule  of  water  at  the  positive  electrode,  and  the  setting 
free  of  one  atom  of  oxygen.  Now,  what  are  the  facts  in  an  actual 
experiment?  If  we  electrolyze  a  solution  of  potassium  or  sodium 
hydroxide  in  water,  we  will  have  two  volumes  of  hydrogen  set  free 
at  the  negative  electrode,  and  one  volume  of  oxygen  at  the  positive 


HISTORICAL  NOTES   AND   CLASSIC   RESEARCHES. 


electrode.  If  our  negative  electrode  consists  of  mercury,  as  in 
Davy's  experiment,  the  sodium  or  potassium  will  amalgamate  with 
the  mercury,  which  prevents  it  from  acting  upon  the  water  so  long 
as  the  current  of  electricity  continues  to  pass.  In  the  experiment 
with  the  block  of  caustic  soda  or  potash  there  would  be  only  sodium 
or  potassium  set  free  in  the  mercury,  and  oxygen  at  the  moist  surface 
of  contact  of  the  caustic  block  and  the  platinum-sheet  base. 

To  electrolyze  such  a  solution  experimentally,  set  up  an  apparatus 
like  that  shown  in  the  next  illustration.  Two  large  test-tubes  may  be 
used,  and  it  will  be  observed  that  just  twice  the  volume  of  hydrogen 


i 


FIG.  4. — Experimental  Electrolysis  of  Sodium  or  Potassium  Hydroxide  Solution.  O, 
oxygen  collected  in  positive  tube;  H,  hydrogen  collected  in  negative  tube;  CCy 
carbons  of  battery;  ZZ,  zincs  of  battery.  Arrows  indicate  the  direction  of  current. 

will  be  set  free;  in  other  words,  two  volumes  of  hydrogen  to  one 
volume  of  oxygen  will  be  liberated.  Where  the  wires  dip  under  the 
caustic  solution  it  will  be  necessary  to  insulate  them  with  a  solution 
of  rubber,  or  else  several  coats  of  gum  shellac,  to  prevent  the  libera- 
tion of  gases  from  the  wires  themselves.  With  the  ends  properly 
insulated,  the  setting  free  of  the  oxygen  and  hydrogen  will  be  confined 
to  the  platinum  plates  within  the  tubes.  Now,  these  platinum  plates 
or  electrodes  have  technical  names,  and  we  must  become  familiar  with 
them.  The  positive  electrode  is  called  the  "anode,"  and  the  negative 
electrode  is  called  the  "cathode."  The  current  in  an  electrolytic 
bath  always  flows  from  the  anode  to  the  cathode,  all  electropositive 
ions  going  to  the  cathode,  and  all  electronegative  ions  going  to  the 
anode.  As  a  general  rule,  all  the  metals  and  hydrogen  go  to  the  cath- 
ode in  an  electrolytic  cell,  and  all  other  chemical  elements  go  to  the 
anode.  The  following  table  shows  the  chemical  elements  arranged 
in  their  electrochemical  order,  some  of  the  extremely  rare  ones  not 
being  included.  In  this  table  each  chemical  element  is  positive  to  any 


10 


EXPERIMENTAL  ELECTROCHEMISTRY. 


element  placed  above  it,  and  negative  to  any  one  given  below  it. 
These  distinctions,  although  of  a  relative  character,  are  very  impor- 
tant, since  it  seems  probable  that  the  very  nature  of  chemical  attrac- 
tion itself  rests  upon  these  electrochemical  relations. 


Anode  or  Positive   Electrode 


Oxygen 

Sulphur 

Negative 
Atoms 

Nitrogen 
Fluorine 
Chlorine 

Bromine 

Iodine 

Selenium 

Phosphorus 

Arsenic 

Chromium 

. 

Vanadium 

Molybdenum 

•>», 

Tungsten 

Boron 

Carbon 

Antimony 

Tellurium 

Tantalum 

Columbium 

Titanium 

Silicon 

Tin 

Hydrogen 

Gold 

Osmium 

Iridium 

Platinum 

Rhodium 

Ruthenium 

Palladium 

Mercury 

Silver 

Copper 

Uranium 

Positive  . 
Atoms 

Bismuth 
Gallium 
Indium  _ 

Germanium 

Lead 

Cadmium 

Thallium 

. 

Cobalt 

Nickel 

Iron 

Zinc 

Manganese  - 

Lanthanum 

Didymium 

Cerium 

Thorium 

Zirconium 

Aluminum 

Scandium 

Erbium 

Ytterbium 

Beryllium 

Magnesium 

Calcium 

Strontium 

Barium 

Lithium 

Sodium 

Potassium 

Rubidium 

i  Caesium 

Cathode  or  Negative  Electrode. 

The  above  column  of  elements  is  arranged  seriatim  as  if  placed 
in  an  electrolytic .  cell. 


HISTORICAL  NOTES   AND   CLASSIC   RESEARCHES.  II 

This  table  very  forcibly  illustrates  the  preponderance  of  positive 
elements  over  negative  elements,  and  also  the  fact  that  we  only 

Jiave  about  seven  simple  negative  ions.     By  a  simple  ion,  a  single 

+ 
charged  atom  like  our  K  is  meant;    a  complex  ion  being  one  like 

OH,  which  is  negative.  Here  we  have  a  negative  atom  and  a  positive 
atom,  composing  a  negative  ion.  In  this  negatively  charged  hydroxyl 
group,  or  hydroxyl  ion,  we  can  think  of  the  hydrogen  striving  to  go 
to  the  cathode,  and  the  oxygen  striving  to  go  to  the  anode,  and  the 
oxygen  having  the  greatest  pull  and  winning,  since  it  is  more  strongly 
electronegative  than  the  hydrogen,  is  electropositive,  as  a  glance  at  the 
table  will  show.  By  means  of  this  table  we  should  be  able  to  pre- 
determine the  polarity  of  a  complex  ion  with  facility. 

For  example,  let  us  take  the  three  acids,  hydrochloric,  sulphuric, 
and  nitric,  and  disolves  them  in  water.     How  do  they  ionize  ?    With 

the  help  of  the  above  table  and  carefully  conducted  experiment  it  is 

+ 

an  easy  matter  to  determine.  The  HC1  gives  H  Cl,  the  H2SO4  gives 
+  +  •  +  - 

H2  SO4,  and  the  HNO3  gives  H  NO3.     Sulphuric  acid  has  been 

i.  _ _        « 

shown  by  the  present  writer  to  also  ionize  into  the  ions  H  HSC>4. 
Here  we  have  a  case  where  hydrogen  goes  to  the  positive  electrode 
or  anode,  but  it  is  drawn  there  by  being  linked  to  two  more  power- 
fully electro-negative  atoms.  There  are  a  few  cases  where  metals 
go  to  the  anode  in  electrolysis,  but  only  under  such  circumstances  as 
the  hydrogen.  No  metal  goes  to  the  anode  in  an  electrolytic  cell, 
unless  it  is  part  of  a  powerful  group  of  electro-negative  atoms.  Now 
if  we  accept  the  theory  of  electrolytic  dissociation,  we  are  led  to 
believe  in  a  number  of  things.  Perhaps  the  most  important  conse- 
quence of  such  a  theory  is  the  fact  that  we  have  actually  moving 
masses  of  matter  in  a  solution  when  an  electric  current  is  made  to 
flow  through  it.  Such  a  solution  of  a  chemical  substance,  capable 
of  conducting  the  electric  current,  is  technically  known  as  an  elec- 
trolyte. In  all  electrolytes,  therefore,  the  passage  of  an  electric 
current  through  it  is  accompanied  by  the  movement  of  ponderable 
particles  of  matter;  in  other  words,  the  atoms  themselves  act  as 
carriers  of  electricity.  There  will  be  an  abundance  of  "  experimental 
evidence"  later  to  show  this,  but  for  the  present  we  must  accept 
the  theory  upon  faith.  As  we  shall  deal  a  great  deal  with  anodes  and 


12 


EXPERIMENTAL   ELECTROCHEMISTRY. 


cathodes,  and  the  direction  of  the  electric  current,  together  with 
its  management  and  application,  the  latter  part  of  the  present  chapter 
will  be  devoted  to  the  more  practical  side  of  the  question. 

SIMPLE    DIAGRAMS    OF    THE    USE    OF    THE    ELECTRIC    CURRENT    FOR 

ELECTROLYSIS. 

Direction  of  the  Electric  Current. — As  we  must  always  know 
the  direction  of  the  electric  current  in  all  our  electrolytic  investi- 
gations, it  does  not  seem  out  of  place  to  introduce  at  this  time 
a  purely  electrolytic  pole-finder,  or  current  indicator.  This  con- 
sists of  a  glass  tube  with  the  ends  bent  up  as  shown  in  Fig.  5, 
and  supported  horizontally  by  a  couple  of  laboratory  stands. 


IWI 


B 


r/.N, 


FIG.  5. — A  and  C,  anode  and  cathode,  respectively,  in  glass  tube;  M,  globule  of  mer- 
cury which  travels  with  the  current;  B,  cell  of  battery  supplying  current;  C  and 
Z,  copper  and  zinc  electrodes  of  battery.  The  arrows  indicate  the  direction  of 
flow  of  the  electric  current,  as  well  as  the  movement  of  the  mass  of  mercury. 

Two  loose-fitting  stoppers  carry  the  platinum-wire  electrodes  con- 
nected to  a  battery,  or  modified  electric-light  current,  or  small 
dynamo.  A  globule  of  mercury  is  placed  in  the  tube  as  indicated 
at  M,  and  the  tube  filled  to  near  the  level  of  the  stoppers  with 
a  dilute  solution  of  sulphuric  acid  in  water.  Upon  closing  the 
circuit,  the  mercury  will  immediately  travel  to  the  negative  pole  or 
cathode.  On  reversing  the  direction  of  the  current,  the  globule  of 
mercury  will  be  propelled  in  the  reverse  direction,  serving  as  a  very 
pretty  illustration  of  the  behavior  of  positive  ions,  and  answering 
all  the  requirements  of  a  pole-finder  or  indicator  of  current  direction, 


HISTORICAL  NOTES  AND    CLASSIC   RESEARCHES.  13 

if  the  current  is  sufficiently  strong.  If  the  mass  of  mercury  is  large 
it  will  require  a  stronger  current  to  move  it,  but  if  quite  small  it 
will  be  propelled  by  about  TV  of  an  ampere.  For  very  feeble  cur- 
rents, the  direction  of  flow  must  be  learned  by  means  of  a  compass- 
needle.  Perhaps  for  all  ordinary  work  there  is  no  source  of  electrical 
current  so  handy  and  satisfactory  as  the  modified  electric-lighting 
current  when  of  the  direct  type,  and  from  no  to  220  volts  pressure. 
The  accompanying  diagram,  Fig.  6,  indicates  the  use  of  such  a  cur- 
rent in  connection  with  an  electrolytic  cell  and  a  lamp-bank,  which 
may  be  placed  in  any  convenient  part  of  the  laboratory  or  workroom. 


"1 


FiG.  6. — Diagram  of  Lamp-bank  and  Electrolytic  Cell  in  Connection  with  a  no-  or 
a  22o-volt  Direct-current  Electric -lighting  Circuit. 

This  lamp-bank,  which  is  the  special  design  of  the  author,  has  proven 
so  useful  in  many  electrochemical  processes  that  an  enlarged  diagram 
of  it  is  given  in  Fig.  7.  When  connected  with  the  no- volt  circuit 
a  i6-candle-power  lamp  inserted  in  any  of  the  single  sockets  A  allows 
about  J  ampere  to  pass.  With  all  eight  of  the  single  sockets  filled, 
it  allows  about  4  amperes  to  flow;  and  if  these  same  sockets  are 
filled  with  3  2 -candle -power  lamps,  a  current  of  about  8  amperes 
will  be  obtained.  Now,  for  a  more  feeble  current,  less  than  J  ampere, 
two  1 6- candle-power  lamps  are  placed  in  the  sockets  BB,  and  a 
current  flow  of  about  -fij^  will  be  obtained.  With  three  of  these 
lamps  in  the  sockets  CCC,  a  current  of  about  TV%-  will  be  allowed  to 
pass;  2 20- volt  lamps  may  be  used  here  in  series,  when  the  current 
will  be  less  than  -jfa  ampere.  This  is  only  in  accordance  with  the 


EXPERIMENTAL  ELECTROCHEMISTRY. 


well-known  law  of  Ohm:  C=R+V,  where  C  is  the  current,  R  the 
resistance,  and  V  the  voltage.  A  3 2 -candle-power  no- volt  lamp  has 
a  resistance  of  about  no  ohms,  a  i6-candle-power  lamp  about  220 
ohms,  and  a  2 20- volt  lamp  about  440  ohms.  So  it  will  be  seen  that 
with  the  three  kinds  of  lamps  at  hand  a  very  flexible  lamp-bank 
results  from  the  design  given. 


0 

FIG.  7. — Laboratory  Lamp-bank  for  Electrolytic  Work.     Range  from  T^  ampere  to 

8  amperes. 

However,  for  certain  work  the  high  potential  of  the  electric- 
lighting  circuit  is  not  desired,  and  the  lamp-bank,  no  matter  how 
designed,  will  not  meet  requirements.  Again,  should  we  require 
20  amperes  of  current  for  certain  work,  the  lamp-bank  would  have 
to  hold  twenty  32-candle-power  lamps,  or  forty  i6-candle-power 
lamps,  and  would  be  very  wasteful  of  energy  when  we  consider 
that  we  are  working  under  a  difference  of  potential  of  at  least  no 
volts;  no  volts X 20  amperes  would  represent  2200  watts,  which 
would  be  nearly  3  horse-power;  2200  watts  divided  by  746  (number 
of  watts  to  the  horse-power)  equal  2.94  horse -power.  Whereas  we 
would  require  the  20  amperes  for  our  electrolysis,  we  could  not  only 
get  along  with  4  volts  pressure,  but  would  actually  prefer  it,  so  we 


HISTORICAL  NOTES   AND    CLASSIC   RESEARCHES.  15 

use  a  motor-generator,  and  consume  something  like  80  watts,  instead 
of  the  2200.  20  amperes  X  4  volts  =  80  watts.  The  photograph, 
Fig.  8,  shows  a  simple  form  of  motor-generator  used  by  the  author 


FlG.  8. — Photograph  of  a  Motor-generator  used  to  Convert  the  no-volt  Lighting 
Current  into  a  i5-ampere  Current  at  4  Volts  Pressure,  which  are  the  ideal  con- 
ditions for  many  electrochemical  processes  for  experimental  purposes. 


FlG.  9. — Diagram  of  Motor-generator  and  Electrolytic  Cell  in  connection  with  Elec- 
trical Measuring-instruments  for  Observing  Electrical  Conditions  within  the 
Electrolyte.  Here  the  comparatively  high-voltage  electric-lighting  current  is 
stepped  down  to  the  ideal  voltage  for  electrolysis  of  chemical  compounds. 

for  the  past  six  or  seven  years,  which  gives  about  20  amperes  at  a 
pressure  of  only  4  volts,  the  driving-motor  taking  a  trifle  more  than 
the  corresponding  number  of  watts. 


it>  EXPERIMENTAL   ELECTROCHEMISTRY. 

The  last  illustration  in  our  present  chapter  is  a  diagram  of  a  similar 
motor-generator,  but  of  the  belted  type,  and  represents  electrical 
measuring  instruments  properly  connected  for  observing  the  watts 
used  in  the  electrolyte  for  any  kind  of  electrolytic  work.  Here  M 
is  the  driving-motor,  G  the  generator,  V  and  A  the  voltmeter  and 
ammeter  respectively,  and  RR  rheostats  for  controlling  the  speed 
of  the  motor  on  the  one  hand  and  the  current  supplied  to  the  elec- 
trolytic cell  on  the  other.  The  generator  is  of  the  shunt-wound 
type,  and  it  is  very  necessary  to  have  a  good  variable  resistance 
in  the  outside  circuit.  The  ammeter  shows  the  current  taken 
and  the  voltmeter  the  drop  of  potential  across  the  electrodes.  Such 
a  small  rotary  converter  can  be  ordered  from  almost  any  of  the 
manufacturers  of  small  dynamos  and  motors.  Having  outlined  the 
simple  apparatus  necessary  for  practical  work  on  a  small  scale,  we 
will  close  the  present  chapter  with  definitions  of  the  technical  terms 
introduced  and  continue  the  development  of  the  subject  in  the 
next  chapter. 

Electrolysis. — The  breaking  up  of  chemical  compounds  by  the 
electric  current,  and  the  setting  free  at  the  electrodes  of  the  con- 
stituents. 

Electrode. — The  terminal  of  the  source  of  electricity  which  dips 
into  the  electrolyte. 

Electrolyte. — A  chemical  compound,  capable  of  conducting  the 
electric  current  when  in  solution  or  in  the  fused  state. 

Anode. — The  positive  electrode  in  an  electrolyte.  The  electrode 
from  which  the  electric  current  flows. 

Cathode. — The  negative  electrode  in  an  electrolyte.  The  elec- 
trode to  which  the  electric  current  flows. 

Ion. — A  chemical  atom  or  group  of  atoms  possessed  of  an  elec- 
trical charge. 

Electrolytic  conductivity. — The  passage  of  the  electric  current 
through  an  electrolyte  accompanied  by  the  movement  of  ponderable 
material.  Ion  transfer.  The  carrying  of  the  electric  current  by 
moving  ions. 

Electrolytic  dissociation. — The  breaking  up  of  certain  chemical 
molecules  when  dissolved  in  water  or  other  suitable  solvents,  into 
ultimate  parts  charged  with  electricity. 


CHAPTER  II. 
THE   THEORY   OF   ELECTROLYTIC   DISSOCIATION. 

IN  the  last  chapter,  that  beautiful  doctrine  known  generally  as 
the  theory  of  electrolytic  dissociation  was  touched  upon,  and  the 
reader  was  asked  to  accept  upon  faith  the  truth  of  its  meaning  for 
the  time  being.  It  is  the  purpose  of  the  present  chapter  to  advance 
some  of  the  best  experimental  evidence  in  its  support,  and  leave  the 
student  to  formulate  his  own  opinions.  Probably  there  is  no  generali- 
zation in  the  entire  domain  of  physical  chemistry  quite  so  unique  and 
attractive  as  the  theory  advanced  as  recently  as  1887  by  Svante 
Arrhenius,  now  professor  at  the  University  of  Stockholm.  Few 
theories  in  either  chemical  or  physical  science  have  been  the  subject 
of  greater  dissertation,  dispute,  or  attack  than  the  dissociation 
theory,  and  few  have  served  a  more  useful  purpose  in  accounting 
for  certain  vital  phenomena.  The  theory  of  electrolytic  dissociation 
has  the  most  excellent  experimental  evidence  in  its  favor,  and  accounts 
perfectly  for  many  heretofore  unexplained  facts,  and  those  urging 
objections  to  its  truth  have  never  been  able  to  propose  a  better  one, 
or  even  one  half  as  good.  It  will  be  the  effort  of  the  present  writer 
to  advance  what  he  considers  to  be  the  best  and  most  forcible  evi- 
dence for  this  doctrine,  and  adopt  it  throughout  in  the  practical 
electrochemical  studies  which  are  to  follow.  Until  something  better 
is  brought  forward,  we  will  not  take  our  time  in  making  attacks 
upon  the  doctrine.  The  arguments  against  the  theory  will  not  be 
introduced  for  fear  of  confusing  the  student.  We  know  from  previous 
experience  that  we  have,  broadly  speaking,  two  kinds  of  conductors 
of  the  electric  current — the  metals  and  alloys  on  the  one  hand,  and 
solutions  of  certain  chemical  substances  on  the  other.  In  the  case 
of  the  metals  and  alloys  they  are  called  conductors  of  the  first  class, 
and  in  the  case  of  chemical  substances  in  solution  or  in  a  state  of 
fusion  they  are  called  conductors  of  the  second  class.  The  passage 

it 


i8 


EXPERIMENTAL   ELECTROCHEMISTRY. 


of  an  electric  current  through  a  conductor  of  the  second  class  is 
believed  to  be  accompanied  by  the  actual  movement  of  ponderable 
material,  or  a  mechanical  transfer  of  matter.  Good  evidence  in 
support  of  this  will  be  introduced  a  little  later. 

We  may  now  take  all  known  chemical  compounds  and  divide  them 
into  two  great  groups  as  follows :  ist.  Those  compounds  which  when 
dissolved  in  water  or  other  suitable  solvent  conduct  the  electric 
current;  2d.  Those  compounds  which  when  dissolved  do  not  conduct 
the  electric  current.  For  this  purpose  we  may  draw  a  dividing  line 
separating  these  two  great  classes,  and  term  those  which  conduct 
when  in  solution,  electrolytes,  and  all  those  which  do  not  conduct 
the  electric  current  when  in  solution,  non-electrolytes.  In  the  follow- 
ing table  a  few  chemical  compounds  of  both  kinds  are  given.  This 
table  could,  of  course,  be  indefinitely  extended,  but  a  sufficient 
number  of  compounds  are  given  to  show  the  character  and  meaning 
of  the  division.  Upon  examining  the  bodies  in  the  left-hand  column 
it  will  be  observed  that  all  the  electrolytes  are  among,  and  constitute, 

CHEMICAL  SUBSTANCES. 


Electrolytes. 


Non-electrolytes. 


Sodium  chloride NaCl 

Sodium  nitrate NaNO3 

Potassium  sulphate K2SO4 

Ammonium  hydroxide NH4OH 

Sodium  hydroxide NaOH 

Potassium  hydroxide KOH 

Sulphuric  acid H2SO4 

Nitric  acid HNO3 

Hydrochloric  acid HC1 

Acetic  acid CH3COOH 

Oxalic  acid CzHjO, 

Silver  nitrate AgNO3 


Cane-sugar 
Ethyl  alcohol 

Methyl  alcohol CH3OH 

Benzene C6H0 

Chloroform CHC13 

Ether (C2H5)2OH 

Acetic  aldehyde CH3CHO 

Formic  aldehyde HCHO 

Acetone CH3COCH9 

Propyl  alcohol C3H5OH 

Amyl  alcohol C5HUOH 

Isopropyl  alcohol CsH7OH 


the  "chemically  active"  bodies,  whereas  the  non-electrolytes  con- 
stitute the  "chemically  inactive"  bodies.  It  will  be  observed  that 
certain  chemical  substances  are  electrolytes  only  when  dissolved 
in  water  or  other  suitable  solvent,  or  when  in  the  fused  condition, 
according  to  the  definition  of  an  electrolyte.  We  may  take  any  of 
the  chemical  compounds  in  the  left-hand  column,  including  even  the 
acids,  and  when  absolutely  water-free  they  are  non-conductors  of 
the  electric  current.  Water  itself,  when  properly  distilled  and  air- 


THE  THEORY   OF   ELECTROLYTIC   DISSOCIATION.  i£ 

free,  is  also  a  non-electrolyte  (except  to  an  infinitesimal  extent),  and 
yet  when  certain  chemical  substances  are  dissolved  in  water  they 
become  most  excellent  conductors  of  electricity.  See  Fig.  10  for  a 
simple  experiment  for  distinguishing  electrolytes  from  non-electrolytes^ 
The  lamp-bank  and  electric -lighting  circuits,  or  the  motor  generator 
as  described  in  the  first  chapter,  may,  of  course,  be  used  instead  of 
the  storage-battery  as  given  here.  Here  we  may  have  the  case  where 
two  bodies,  when  separated,  each  prove  to  be  non-conductors,  and 
when  brought  together,  to  conduct  highly  the  electric  current.  What 
is  it  due  to  ?  To  take  a  special  case,  a  crystal  of  rock  salt  (sodium 
chloride)  and  carefully  distilled  water.  Neither  of  these  substances 
will  conduct  the  electric  current  to  any  appreciable  extent.  Dissolve 


n  ri 


B  B  A 

FIG.  10. — Simple  Apparatus  for  Distinguishing  Electrolytes  from  Non-electrolytes. 
A ,  glass  beaker  containing  distilled  water  with  platinum  electrodes  into  which  the 
compound  to  be  tested  is  dropped;  C,  milli -amperemeter;  BB,  cells  of  storage- 
battery.  There  is  always  a  slight  indication  of  conductivity  upon  a  sensi  ive 
milli-amperemeter  when  only  the  glass  beaker  and  distilled  water  are  present,, 
due  to  the  dissolving  of  a  minute  trace  of  glass  together  with  impurities  in  the 
distilled  water.  The  amount  of  deflection  can  be  noted  and  applied  as  a  cor- 
rection. 

the  salt  in  the  water  and  the  solution  has  a  high  conductivity.  Some- 
thing must  have  taken  place  within  the  water,  and  yet  we  know  we 
have  made  only  a  simple  solution  of  salt  in  water,  which  when. 
evaporated  to  dryness,  gives  back  our  salt  unaltered,  and  if  we  catch, 
and  condense  the  water  driven  off,  we  have  ordinary  distilled  water 
again.  What  is  the  condition  of  the  salt  in  the  water,  then,  to  so  greatly 
change  its  physical  behavior  toward  the  electric  current?  In  terms 
of  the  theory  of  electrolytic  dissociation,  as  was  pointed  out  in  the 
previous  chapter,  the  chemical  molecule  is  broken  up  into  "ions"" 
or  ultimate  parts,  and  these  ultimate  parts  bear  electrical  charges 
upon  them.  The  molecular  formula  of  sodium  chloride  is  represented 
simply  thus,  NaCl,  so  familiar  to  all  general  chemists.  Now  upon 
immersion  in  water  the  molecule  is  believed  to  be  broken  up  as- 


£0  EXPERIMENTAL    ELECTROCHEMISTRY. 

4- 

follows  into  two  "ions,"  Na  and  Cl,  the  bond  or  attraction  between 
the  two  former  atoms  being  broken,  and  the  sodium  ion  with  its 
'electrical  charge  is  existing  independently  of  the  chlorine  ion  with 
its  electrical  charge  of  unlike  polarity  or  sign.  The  mere  act  of 
passing  into  solution  is  believed,  in  terms  of  our  theory,  to  separate 
the  atoms  of  certain  molecules,  the  atoms  becoming  ions  at  once 
by  taking  upon  themselves  electrical  charges  of  opposite  signs,  the 
one  becoming  a  positive  ion,  the  other  a  negative  ion.  In  the  previous 
chapter  it  was  pointed  out,  by  means  of  a  diagram,  that,  the  positive 
ion  traveled  to  the  negative  electrode,  and  that  the  negative  ion 
traveled  toward  the  positive  electrode.  It  is  the  purpose  of  this 
chapter  to  show  that  we  have  excellent  reasons  for  believing  in  the 
-existence  of  these  electrically  charged  particles  when  certain  chemical 
substances  are  dissolved  in  water.  We  will  take  up  the  study  of 
the  evidence  first  by  comparing  the  deportment  of  substances  in 
aqueous  solution  with  substances  in  the  state  of  a  gas,  and  for  this 
purpose  we  will  first  set  down  the  three  gas  laws  so  well  known  to  ail 
students  of  modern  chemistry  and  physics. 

Law  of  Boyle.  The  pressure  exerted  by  a  gas,  the  temperature 
remaining  the  same,  is  proportional  to  the  concentration  of  the  gas. 
The  concentration  of  the  gas  is  directly  proportional  to  the  number 
of  molecules  or  ultimate  parts  of  molecules  present. 

Law  of  Gay-Lussac.  The  pressure  of  a  gas  increases  a  constant 
amount  for  every  increase  of  i°  in  temperature,  and  the  increase  in 
pressure  is  equal  to  -^  of  the  original  pressure  of  the  gas  at  o°  C. 

Law  of  Avogadro.  Equal  volumes  of  all  substances  in  the 
gaseous  state,  under  the  same  conditions  of  temperature  and  pressure, 
contain  the  same  number  of  molecules  or  ultimate  parts  of  molecules. 

Consequently  the  molecules  of  all  substances,  or  the  ultimate 
parts  of  all  molecules  when  in  the  gaseous  state,  under  the  same 
conditions  of  temperature  and  pressure,  occupy  the  same  space. 

Having  the  three  fundamental  gas  laws  before  us,  we  will  take 
them  up  separately  in  the  order  given,  and  learn  what  bearing  they 
have  upon  the  behavior  of  substances  in  solution.  What  possible 
application  can  these  gas  laws  have  to  chemical  compounds  dissolved 
,in  water?  There  appears  to  the  general  student  to  be  no  connection 
.whatever,  and  yet  there  is  the  most  vital  application  of  the  gas  laws 
in  support  of  the  theory  of  electrolytic  dissociation.  Let  us  fir:t 


THE   THEORY   OF   ELECTROLYTIC   DISSOCIATION.  21 

take  up  Boyle's  law,  which  has  to  do  with  the  pressure  exerted  by 
substances  in  the  state  of  a  gas.  This  tells  us  facts  based  upon 
experimentally  determining  the  pressures  exerted  by  gases  of  differ- 
ent concentrations.  The  pressures  of  gases  confined  in  given  volumes, 
at  constant  temperature  can  be  readily  measured  by  manometers 
or  pressure-gauges,  as  set  forth  in  detail  in  any  good  text-book  on 
physics.  This  we  know;  but  can  we  measure  the  pressures  exerted 
by  substances  in  solution  ?  We  can  convert  a  given  mass  of  a  given, 
substance  into  a  gas  by  heating,  and  measure  the  pressure  at  differ- 
ent concentrations,  or  volumes,  by  means  of  suitable  manometers- 
If  we  dissolve  the  same  quantity  of  the  compound  in  water,  will  the 
molecules  exert  a  pressure  in  the  dissolved  condition,  and  can  we 
measure  it  ?  Both  these  questions  can  be  answered  in  the  affirmative,, 
and  it  is  the  purpose  here  to  show  that  such  pressures  exist,  and  to> 
describe  how  they  may  be  measured.  All  substances  when  dissolved 
in  water  exert  a  pressure,  and  this  pressure  has  been  termed  "osmotic 
pressure." 

OSMOTIC   PRESSURE   AND   METHOD   OF   MEASURING   IT. 

If  a  gas,  oxygen  or  hydrogen  for  example,  be  liberated  in  a  given 
space,  the  gas  will  expand  in  all  directions  and  completely  fill  the 
containing  vessel.  If  all  parts  of  this  containing  vessel  are  at  the 
same  temperature,  the  gas  will  expand  and  distribute  itself  uni- 
formly throughout  the  volume.  There  will  be  repellent  forces 
between  the  molecules  of  the  gas,  driving  them  to  the  remotest  recesses 
of  the  containing  vessel,  and  consequently  there  will  be  a  pressure 
against  the  walls  of  the  same.  The  more  concentrated  the  gas,  or,, 
in  other  words,  the  greater  the  number  of  molecules  or  ultimate 
parts  of  molecules  present,  the  greater  will  be  the  pressure  within  the 
fixed  or  given  volume.  What  can  be  said  about  substances  in  solu- 
tion? The  behavior  is  the  same.  Let  us  take  a  large  vessel  of 
water,  for  example  a  tall  glass  jar  full,  and  introduce  a  little  sugar  in. 
it.  The  sugar  will  immediately  fall  to  the  bottom,  a  small  portion, 
dissolving  and  passing  into  solution  on  the  way  down.  "What  will 
b3  the  ultimate  result  on  standing?  The  sugar  at  the  bottom  will 
all  pass  into  solution,  rise  against  gravity,  and  in  time  distribute 
i;self  uniformly  throughout  the  solvent.  The  sugar  in  the  dissolved 
state  will  behave  exactly  as  it  would  when  in  the  state  of  a  gas,  and 


-22  EXPERIMENTAL   ELECTROCHEMISTRY. 

will  exert  a  pressure  when  in  solution  which  may  be  measured.  This 
is  due  to  the  phenomenon  of  diffusion,  which,  not  so  many  years  ago, 
was  wholly  unaccounted  for.  Here  we  have  a  heavy  substance  dis- 
solving at  the  bottom  of  a  tall  glass  cylinder  filled  with  water,  and 
rising  to  the  top  against  the  attraction  of  gravity.  There  is  a  pres- 
sure, and  this  pressure  has  only  recently  been  accounted  for.  Another 
phenomenon  which  until  recently  could  not  be  explained  was  the 
bursting  of  an  animal  bladder,  filled  with  a  mixture  of  alcohol  and 
water,  when  immersed  in  a  vessel  containing  pure  water.  The 
ibladder  under  these  conditions,  if  it  has  been  closed  up  properly  at 
the  openings,  will  be  burst  by  a  gradually  developed  pressure  within. 
"It  is  easy  to  show  in  this  way  that  we  have  a  pressure,  and  this  pres- 
sure has  been  termed  osmotic  pressure.  This  is  only  a  very  crude 
method  of  showing  qualitatively  that  we  have  a  positive  pressure,  and 
It  does  not  seem  to  have  occurred  to  the  earliest  workers  that  this  pres- 
sure was  a  definite  thing  and  could  be  quantitatively  measured. 
This  osmotic  pressure  is  a  very  peculiar  thing  when  one  considers 
the  manner  in  which  the  pressure  is  measured.  We  cannot  place  a 
solution  within  a  closed  vessel  and  get  an  indication  of  pressure 
upon  a  gauge-glass  or  manometer,  as  we  very  well  know,  but  must 
Tesort  to  some  kind  of  a  membrane,  such  as  forms  the  animal  bladder. 
'Strange  to  say,  the  pressure  developed  depends  upon  a  differential, 
or  selective  action,  so  to  speak,  of  the  necessary  membrane.  It  must 
allow  the  solvent  to  pass  through,  but  not  the  dissolved  substance,  a 
sort  of  filter,  roughly  speaking,  and  because  of  this  principle  the 
membrane  has  been  called  "semipermeable."  Now  if  we  can 
Teally  produce  a  semipermeable  membrane  or  diaphragm,  we  will 
be  able  to  measure  the  pressure  due  to  substances  in  solution.  Take, 
for  example,  a  solution  of  cane-sugar.  If  we  have  at  hand  a  membrane 
which  will  be  permeable  to  water  and  impermeable  to  sugar,  we 
can  by  its  use  ascertain  the  pressure  due  to  the  presence  of  the  sugar 
molecules,  and  demonstrate  how  this  pressure  varies  with  concen- 
tration of  the  solution  and  with  changes  in  temperature.  We  have 
at  hand,  in  other  words,  means  for  comparing  the  behavior  of  gas 
molecules  with  the  behavior  of  molecules  in  solution.  Let  us  pre- 
pare such  a  semipermeable  membrane  in  the  laboratory  and  examine 
some  of  the  compounds  given  in  the  preceding  table  constituting 
-electrolytes  on  the  one  hand  and  non-electrolytes  on  the  other. 


THE   THEORY   OF   ELECTROLYTIC  DISSOCIATION.  23 

The  accompanying  photograph  illustrates  some  simple  forms  of 
porous  pots,  and  Fig.  12  gives  a  section  through  such  a  typical  pot, 
as  well  as  a  completed  piece  of  apparatus  for  experimentally  measuring 
osmotic  pressure.  Moritz  Traube,  and  Pfeffer,  the  celebrated  plant 
physiologist,  were  the  first  to  discover  and  make  use  of  the  properties 
of  semipermeable  membranes.  It  is  to  Pfeffer  that  we  owe  the 
first  really  serviceable  artificial  semipermeable  diaphragm  or  partition. 


FIG.  ii. — Some  Forms  of  Porous  Pots  with  Semipermeable  Membranes  for  the 
Measurement  of  "Osmotic  Pressure."  The  broken  exhibit  shows  the  semi- 
permeable  membrane  at  M . 

It  was  discovered  by  Pfeffer  that  plant  and  animal  membranes  could 
be  discarded,  and  that  certain  chemical  precipitates,  when  properly 
supported,  met  the  requirements  almost  perfectly.  Copper  ferro- 
cyanide  was  found  to  give  the  most  satisfactory  results  when  formed 
right  in  the  walls  of  a  very  fine-grained  unglazed  porous  pot.  In 
order  to  produce  such  a  precipitate  within  the  walls  of  the  porous 
pot,  it  was  filled  with  a  solution  of  potassium  ferrocyanide  and  im- 
mersed in  a  solution  of  copper  sulphate.  The  two  solutions  met 
within  the  walls  and  there  formed  the  semipermeable  membrane 
with  the  resistant  support  of  the  porous  pot.  When  such  a  prepared 


24  EXPERIMENTAL   ELECTROCHEMISTRY. 

pot  is  broken  open,  the  membrane  appears  in  the  form  of  a  fine  line, 
as  indicated  in  Fig.  1 1  at  M'.  There  are  many  necessary  precautions 
to  be  taken  in  the  preparation  of  successful  semipermeable  mem- 
branes, it  being  an  art  requiring  not  a  little  patience  and -skill. 
The  following  is  taken  from  one  of  Pfeffer's  writings  on  the  subject  : 
"The  porcelain  cells  were  first  completely  injected  with  water  under 
the  air-pump  and  then  placed  for  at  least  some  hours  in  a  solution 
containing  at  least  3  per  cent  of  copper  sulphate,  and  the  interior 
was  also  filled  with  this  solution.  The  interior  only  of  the  porcelain 
cell  was  then  rinsed  out  quickly  with  water,  well  dried  as  rapidly  as 
possible  by  introducing  strips  of  filter-paper,  and  after  the  outside 
had  dried  on;,  it  was  allowed  to  stand  some  time  in  the  air  until  it 
just  felt  moist.  Then  a  3  per  cent  solution  of  potassium  ferrocyanide 
was  poured  into  the  cell  and  this  immediately  reintroduced  into  the 
solution  of  copper  sulphate.  After  the  cell  had  stood  undisturbed 
for  from  twenty-four  to  forty-eight  hours,  it  was  completely  filled 
with  the  solution  of  potassium  ferrocyanide  and  closed.  ...  A 
certain  excess  of  pressure  of  the  contents  of  the  cell  now  gradually 
manifested  itself,  since  the  solution  of  potassium  ferrocyanide  had  a 
greater  osmotic  pressure  than  the  solution  of  copper  sulphate.  After 
another  twenty-four  to  forty-eight  hours  the  apparatus  was  again 
opened  and  generally  a  solution  introduced  which  contained  3  per 
cent  of  potassium  ferrocyanide  and  ij  per  cent  of  potassium  nirate 
(by  weight),*  and  which  showed  an  excess  of  osmotic  pressure  of 
somewhat  more  than  three  atmospheres." 

In  all  this  work  as  reproduced  by  the  present  writer  is  was  found 
most  essential  to  obtain  a  special  close-grained  grade  of  porous  cup 
or  pot.  A  common  porous  pot,  or  one  the  least  faulty,  such  as 
containing  minute  invisible  fissures,  will  defeat  the  object  of  the  entire 
experiment-^  With  faulty  pots  the  writer  has  frequently  had  a  com- 
pleted piece  of  apparatus  assembled,  indicating  a  height  of  only  2  or 
3  feet  of  the  contained  solution,  when  the  semipermeable  membrane 
gave  way  and  oozed  through  the  side  of  the  porous  pot.  It  has  been 
found  that  a  dilute  solution  of  cane-sugar  in  water  would  rise  to  a 
height  of  66  feet.  Referring  once  more  to  Fig.  12,  we  will  note  a  rise 
of  about  2  feet,  a  one-half  normal  sugar  solution  being  used  in  this 
case.  Strange  as  it  may  seem,  the  sugar  solution  is  placed  within 
the  porous  pot  A  and  the  pot  is  in  turn  immersed  in  the  beaker  B, 


THE   THEORY  OF  ELECTROLYTIC   DISSOCIATION.  25 

containing  distilled  water.    The  pressure  is  developed  within  the 
porous  pot  by  a  very  curious  action,  forcing  the  liquid  up  into  the 


FIG.  12.— -4,  porous  pot;  B,  glass  beaker;  C,  tight-fitting  stopper;  D,  height  to 
which  the  contained  solution  has  risen;  E,  graduated  scale;  F,  transverse  sec- 
tion of  porous  pot;  S,  semipermeable  membrane  within  the  Wall  of  the  pot; 
G,  enlarged  vertical  section  through  porous  pot  with  semipermeable  membrane 
showing  at  5. 

manometer- tube.  The  conditions  are  as  follows:  The  semiper- 
meable membrane  allows  water  to  pass  through  freely,  but  does 
not  allow  the  sugar  molecules  to  pass.  Within  we  have  sugar 


26  EXPERIMENTAL  ELECTROCHEMISTRY. 

molecules  and  water  molecules  attempting  to  get  out,  and  out- 
side we  have  all  water  molecules  attempting  to  get  in.  Now, 
we  have,  per  unit  area  of  the  porous  pot  and  semipermeable 
membrane,  a  more  effective  bombardment  from  the  pure-water 
molecules  without  than  from  the  mixed  molecules  within.  We 
may  think  about  the  thing  also  as  follows:  Every  water  molecule 
striking  the  diaphragm  from  the  outside  gets  in,  but  many  of  the 
water  molecules  before  striking  the  diaphragm  from  the  inside 
collide  with  sugar  molecules,  which  cannot  get  through,  and  thereby 
their  effectiveness  is  lost.  As  a  result  of  such  a  differential  action 
we  may  have  a  slow  ingress  of  water  molecules  tending  to  dilute  the 
sugar  by  driving  its  molecules  farther  apart  and  thereby  establishing 
a  pressure.  Let  us  leave  the  theory  of  the  apparatus  now  and  look 
at  the  facts  in  some  actual  and  carefully  conducted  experiments. 

OSMOTIC   PRESSURE    OF   NON-ELECTROLYTES   AND   ELECTROLYTES. 

For  the  sake  of  simplicity  we  will  record  the  result  of  an  osmotic- 
pressure  determination  upon  a  non-electrolyte.  For  this  purpose  we 
will  choose  the  first  non-electrolyte  appearing  at  the  top  of  the  column 
in  the  little  table  already  given.  This  is  ordinary  cane-sugar,  a 
solution  of  which  in  water  does  not  conduct  the  electric  current. 
The  following  table  shows  the  result  of  one  of  Pfeffer's  carefully 
conducted  determinations  upon  this  substance: 


CANE-SUGAR, 

Concentration  in  Osmotic  Pressure  in 

Per  Cent  by  Weight.  Millimeters  of  Mercury. 

1  ..................................         535 

2  .  .  .•  ...............................  IOl6 

4  ..................................        2082 

6     %      ..................................       3075 

Let  us  now  examine  the  figures  standing  for  osmotic  pressures  and 
interpret  their  meaning. 

Concentration,  Pressure,  P. 

C.  P.  C. 

1  per  cent  535  535 

2  "      "  1016  508 
4    "      "                       2082  521 
6    "      "                       3075  5i3 

In  the  above  table  the  pressure  in  each  case  has  been  divided  by  the 
concentration   with    practically   a   constant    resulting.     What    little 


THE  THEORY   OF   ELECTROLYTIC   DISSOCIATION. 


27 


discrepancy  exists  is  due  to  experimental  error.  Here  we  have  an 
analogy  with  the  law  of  Boyle  as  applied  to  gases.  We  know  that  the 
pressure  of  a  gas  increases  with  its  concentration  in  a  direct  proportion, 
and  we  see  from  the  above  tabulated  data  that  the  osmotic  pressure 
of  a  solution  increases  directly  with  its  concentration.  In  experi- 
mental work  of  this  character  there  are  naturally  sources  of  error 
which  must  be  expected.  For  example,  when  we  start  with  a  i  per 
cent  sugar  solution  and  begin  to  measure  its  osmotic  pressure  by 
such  a  piece  of  apparatus  as  described,  the  solution  is  weakened  by 
the  inflow  of  water,  and  unless  the  manometer-tube  is  very  small,  the 
volume  of  sugar  solution  rising  to  make  the  indication  will  constitute 
a  high  percentage  of  the  entire  volume  in  the  porous  cup.  Pfeffer 
also  showed,  at  the  instigation  of  Van't  Hoff,  that  the  osmotic  pres- 
sure of  solutions  increases  slowly  with  rise  in  temperature,  and  that 
this  pressure  is  analogous  to  the  increasing  pressure  of  a  gas  as  set 
forth  in  the  law  of  Gay-Lussac.  Here  a  solution  of  sugar  was  taken 
again,  but  instead  of  varying  its  percentage  strength  the  temperature 
of  the  solution  was  gradually  increased.  For  this  purpose  a  one- 
tenth  normal  sugar  solution  was  employed  (a  normal  solution  of  cane- 
sugar  is  made  by  dissolving  a  gram-molecular  weight  of  this  com- 
pound in  a  liter  of  water.  A  one-tenth  normal  solution  is  made  by 
dissolving  the  gram-molecular  weight  in  10  liters  of  water),  gradually 
increasing  its  temperature.  The  accompanying  table  shows  the 
data  of  an  actual  experiment. 


Osmotic  Pressure  in  Cm.  of 

Mercury. 

Temperature. 

Calculated 

Experimental. 

from  Gas  Law 
of  Gay-Lussac. 

6.8° 

50.5 

50-5 

13-5° 

52.1 

51-7 

14-2° 

53-i 

51.8 

22.0° 

54.8 

53-2 

While  there  are  slight  discrepancies  due  to  experimental  error, 
the  striking  application  of  Gay-Lussac's  law  to  substances  in  solu- 
tion is  to  be  noted.  Although  Pfeffer  was  the  first  to  successfully 
measure  osmotic  pressures,  it  remained  for  Van't  Hoff  to  bring  out 
the  striking  agreements  with  the  gas  laws  already  set  forth.  Having 


28  EXPERIMENTAL   ELECTROCHEMISTRY. 

observed  the  strong  tendency  of  solutions  to  behave  like  substances 
in  the  state  of  a  gas,  by  experimenting  with  semipermeable  mem- 
branes this  great  Dutch  scientist  investigated  other  possibilities  for 
showing  analogies,  among  them  being  what  is  known  in  physical 
chemistry  as  the  "Principle  of  Soret." 

The  Principle  of  Soret. 

If  a  vertical  glass  tube  is  filled  with  a  solution  of  a  chemical 
compound,  such  as  copper  sulphate  in  water,  for  example,  and  the 
two  ends  of  the  tube  are  kept  at  different  temperatures,  the  copper 
sulphate  will  eventually  become  more  dilute  where  the  temperature 
is  highest  and  more  dense  where  the  temperature  is  lowest.  This 
distribution  of  the  dissolved  molecules  by  diffusion  due  to  differences 
in  temperature  is  known  as  the  principle  of  Soret.  The  apparatus 
shown  in  Fig.  1 3  is  the  design  of  the  present  writer  for  bringing  about 
such  concentration  changes.  The  tubes  filled  with  various  solutions 
were  allowed  to  stand  for  a  long  time  with  the  top  and  bottom  at 
different  temperatures,  when  some  of  the  solution  was  allowed  to 
run  out  from  the  bottom  and  analyzed  for  density,  and  some  of  the 
solution  drawn  out  from  the  top  by  means  of  a  pipette  and  also  ana- 
lyzed for  density.  The  early  experiments  showed  smaller  differences 
in  concentration  than  would  be  called  for  if  Gay-Lussac's  law  applied 
to  the  temperature  coefficient  of  the  osmotic  pressure  of  solutions. 
The  tubes  were  then  allowed  to  stand  for  longer  periods  of  time, 
with  the  result  that  the  figures  obtained  approached  closer  and  closer 
to  the  value  expected  from  the  law  pertaining  to  gases.  Diffusion 
of  molecules  takes  place  very  slowly  and  the  tubes  had  to  stand  for 
many  weeks  undisturbed  before  an  equilibrium  was  finally  established. 
In  one  experiment  where  the  tubes  stood  for  about  twelve  weeks  a 
copper-sulphate  solution  gave  the  following  results: 

Upper  end  of  tube  80°  C. ;  lower  end  of  tube  20°  C.  The  differ- 
ence in  density  between  the  respective  ends  of  the  tube  upon  analysis 
was  found  to  be  14.03  per  cent.  The  difference  in  density  calculated 
from  the  law  of  Gay-Lussac  is  14.3  per  cent.  Another  experiment 
gave  24.87  per  cent  change  in  concentration  when  according  to 
Gay-Lussac's  law  the  figure  should  have  been  24.8  per  cent. 

Here  the  application  of  Gay-Lussac's  law  to  the  behavior  of 
compounds  in  solution  is  very  striking.  With  the  apparatus  as 


THE  THEORY   OF   ELECTROLYTIC   DISSOCIATION.  29 


FIG.  13.— The  "Principle  of  Soret"  (Author's  Apparatus).  A,  vertical  glass  tube  con- 
taining the  substance;  B,  water  in  wooden  tub;  C,  outer  wood  casing  to  be  filled 
in  between  with  charcoal  or  sawdust;  D,  thermometer;  E,  heavy  layer  of  hair- 
felt  between  thick  boards  supporting  top  of  apparatus;  F,  water  in  copper  heater; 
G,  ring  gas-burner  for  heating  water;  H,  bulb  of .  air-thermostat  for  holding 
temperature  of  water  constant;  7,  mercury  of  air-thermostat  for  cutting  off  gas- 
supply,  /,  if  the  temperature  rises  too  high;  K,  long  vertical  glass . condensing- 
tube  to  prevent  loss  of  water,  F,  by  distillation;  L,  thermometer  for  observing 
temperature. 


30  EXPERIMENTAL   ELECTROCHEMISTRY. 

illustrated,  the  large  mass  of  water  in  the  wooden  tub,  together  with 
a  laboratory  kept  at  practically  constant  temperature,  the  lower  end 
of  the  tube  is  'consequently  very  uniformly  maintained  in  tempera- 
ture. The  upper  end  of  the  tube  is  kept  at  an  elevated  temperature 
by  means  of  the  ring  gas-burner  and  the  sensitive  air-bulb  thermostat. 
The  expansion  of  the  air  contained  in  the  air-bulb  H  forces  the 
mercury  at  /  up  to  the  tube  /  which  is  slotted,  and  gradually  cuts 
off  the  supply  of  gas  which  enters  as  indicated  by  the  small  arrow* 
Should  the  temperature  of  the  water  F  fall  below  the  required  tempera- 
ture, the  air  in  the  bulb  H  will  contract  and  allow  the  mercury  to  fall 
away  from  the  tube  /,  thus  uncovering  the  slot  and  allowing  more 
gas  to  flow  to  the  burner.  Two  very  sensitive  thermometers  give 
the  readings  for  the  top  and  bottom  of  the  tube  respectively.  The 
apparatus  is  so  designed  that  the  top  portion  may  be  lifted  off,  when 
the  tube  containing  the  solution  experimented  upon  may  be  readily 
removed.  It  remains  now  to  compare  the  behavior  of  substances  in 
solution  with  the  third  and  last  gas  law,  namely,  that  of  Avogadro. 
This  was  also  done  by  the  chemist  Van't  Hoff.  He  worked  again 
with  a  solution  of  cane-sugar,  and  compared  the  osmotic  pressure  of 
such  a  solution  with  a  volume  of  hydrogen  gas  of  equal  concentration. 
For  this  purpose  he  made  a  cane-sugar  solution  having  the  same 
number  of  sugar  molecules  in  a  given  volume  of  solution  as  there  are 
hydrogen  molecules  in  the  same  volume  of  the  gas.  The  experiment 
fully  justified  the  statement  that  the  sugar  solution  gave  an  osmotic 
pressure  equal  to  the  gas  pressure.  We  may  then  say  that  equal 
volumes  0}  all  chemical  compounds  in  solution  giving  the  same  osmotic 
pressure  at  the  same  temperature  contain  the  same  number  oj  molecules 
or  ultimate  parts  oj  molecules.  Now  this  is  only  true  for  di  ute  solu- 
tions. Very  concentrated  solutions  of  chemical  substances  do  not 
obey  the  law,  and  when  we  look  about  we  are  struck  by  the  fact  that 
very  densely  compressed  gases  do  not  obey  the  law  of  Boyle.  This 
makes  our  comparisons  all  the  more  striking,  for  where  we  have 
exceptions  in  the  case  of  gases,  we  also  have  exceptions  in  the  case  of 
solutions.  It  has  now  been  shown  that  the  three  fundamental  gas 
laws  apply  to  compounds  in  a  state  of  solution,  but  what  has  this, 
although  striking  and  of  vital  interest  to  the  physical  chemist,  to  do 
with  the  theory  of  electrolytic  dissociation  ?  To  answer  this  let  us 
turn  once  more  to  the  first  table  of  this  chapter  where  we  have 


THE  THEORY  OF   ELECTROLYTIC  DISSOCIATION.  31 

electrolytes  on  the  one  hand  and  non-electrolytes  on  the  other.  It  was 
pointed  out  that  all  those  bodies  have  been  classified  according  to  their 
ability  to  conduct  the  electric  current.  All  those  on  the  left  conduct 
when  in  solution,  and  all  those  on  the  right  do  not.  All  those  on  the 
left  are  called  electrolytes,  and  in  terms  of  the  theory  of  electrolytic 
dissociation,  their  molec  les  break  up  into  ions,  each  ion  of  course 
being  an  ultimate  part  of  a  molecule.  Now  as  a  matter  of  fact,  only 
the  non-electrolytes,  when  dissolved  in  water,  obey  the  gas  laws. 
It  is  only  the  non-electrolytes  which  give  an  osmotic  pressure  com- 
parable with  substances  in  the  state  of  a  gas,  the  electrolytes  all  giving 
an  abnormally  high  osmotic  pressure.  This  is  just  what  we  would 
expect  if  one  molecule  breaks  up  into  two  ultimate  parts  and  each 
ultimate  part  occupies  the  same  space  as  the  original  molecule. 
Our  sugar  molecule  does  not  conduct  the  electric  current  when  in 
solution,  it  does  not  break  up  into  ions,  and  gives  as  evidence  a  normal 
osmotic  pressure.  Our  sodium  chloride,  or  common  salt,  does  con- 
duct the  electric  current  when  dissolved,  and  it  gives  an  abnormally 
high  osmotic  pressure.  Of  course  in  comparing  the  osmotic  pressure 
of  sugar  with  sodium  chloride,  two  solutions  are  made  in  which  the 
same  number  of  molecules  are  dissolved  in  each  case.  In  order  to 
accomplish  this  the  gram-molecular  weight  of  each  compound  is 
taken.  By  gram-molecular  weight  of  a  compound  we  mean  the 
molecular  weight  of  the  substance  expressed  in  grams.  For 
example,  the  gram-molecular  weight  of  sodium  chloride  is  58.5 
grams,  58.5  being  the  molecular  weight  of  sodium  chloride.  So 
much  for  the  theory  of  electrolytic  dissociation  and  the  gas  laws  and 
the  evidence  that  the  measurement  of  osmotic  pressure  gives  us  in 
favor  of  ionization.  We  will  take  up  additional  evidence  in  support 
of  the  theory  of  electrolytic  dissociation  in  our  next  chapter. 


CHAPTER   III. 
THE  THEORY  OF  ELECTROLYTIC  DISSOCIATION   (Continued). 

IT  is  well  known  that  pure  water  freezes  constantly  at  o°  C.,  and 
that  this  fact  has  been  made  the  basis  for  the  several  thermometric 
scales  for  scientific  purposes  throughout  the  world.  It  has  also 
been  well  known  from  very  early  times  that  the  addition  of  salts  or 
other  soluble  material  to  water  causes  it  to  freeze  at  a  lower  tempera- 
ture. Every  schoolboy  knows  that  common  sea-water  will  not 
freeze  except  at  very  low  temperatures,  but  few  of  us  who  have  not 
paid  attention  to  physical  chemistry  have  given  the  fact  more  than 
a  passing  thought.  We  know  that  substances  in  solution  cause 
pure  water  to  freeze  at  a  lower  temperature  than  pure  water 
alone;  in  other  words,  that  the  freezing-point  is  lowered  by  the 
presence  of  dissolved  substances.  This  is  purely  qualitative  knowl- 
edge, so  to  speak,  and  there  remains  for  us  to  investigate  this  matter 
quantitatively,  to  see  how  much  solutions  of  the  same  concentration 
lower  the  freezing-point,  and  if  all  compounds  lower  it  equally. 
Raoult,  the  celebrated  French  chemist,  took  up  this  matter  for  experi- 
mental investigation,  and,  to  make  a  long  story  short,  found  that  all 
non-electrolytes  of  equal  concentration  lowered  the  freezing-point  of 
pure  water  to  the  same  extent.  Raoult  worked  with  solutions  con- 
taining one  gram-molecule  of  the  dissolved  substance  per  liter  and 
found  that  the  lowering  of  the  freezing-point  was  the  same,  being 
1.85°  C.  One  gram-molecule  of  a  substance  per  liter  is  a  normal 
solution,  and  we  may  say  therefore  that  all  normal  solutions  of  non- 
electrolytes  lower  the  freezing-point  of  water  1.86°  C.  This  is- com- 
parable to  saying  that  the  lowering  of  the  freezing-point  of  pure 
water  is  dependent  upon  the  number  of  molecules  or  ultimate  parts 
of  molecules  present.  This  is,  of  course,  an  interesting  fact,  but 
what  has  it  to  do  with  the  theory  of  electrolytic  dissociation  ?  This 
question  can  be  very  quickly  answered  by  determining  the  lowering 

32 


THE   THEORY   OF   ELECTROLYTIC   DISSOCIATION.  33 

of  the  freezing-point  by  normal  solutions  of  electrolytes.     What 
would  we  expect  if  the  theory  of  electrolytic  dissociation  be  true? 
Will   a  gram-molecule    of   an    electrolyte   dissolved    in   a   liter   of 
water  give  us  the  same  depression  of  the  freezing-point,  namely, 
1.86   C.  ?    This  was  done  by  Raoult,  and  it  was  found  that  in  every 
case  of  an  electrolyte  the  depression  of  the  freezing-point  was  greater 
than  1.86°  C.     It  will  be  remembered  that  all  electrolytes  exerted 
a  greater  osmotic  pressure  than  non-electrolytes,  and  now  we  see  that 
all  electrolytes  lower  the  freezing-point  to  a  greater  extent  than  non- 
electrolytes.     We  can  only  account  for  these  striking  phenomena  by 
attributing  the  abnormal  behavior  of  electrolytes  to  the  breaking  up 
of  the  molecules,  upon  dissolving,  into  ions.     The  practical  student, 
upon  reading  the  work  done  by  Raoult  and  noting  his  constant  of 
1.86°  C.,  will  want  to  know  how  much  greater  the  depression  of  the 
freezing-point  was  found  to  be  in  the  case  of  electrolytes,  and  what 
kind  of  a  thermometer  was  employed  when  dealing  with  such  small 
differences  in  temperature.     The  average  electrolyte,  when  dissolved 
in  water,  depresses  the  freezing-point  about  twice  as  much  as  any 
non-electrolyte.    As  for  the  thermometer,  it  is  far  from  the  ordinary 
pattern,  and  is  used  in  a  special  piece  of  apparatus.     The  best  and 
most  universally  used  apparatus  is  that  of  Beckmann,  and  is  illustrated 
in  one  of  its  forms  in  Fig.  14.     The  thermometer  in  this  particular 
case  is  simply  one  of  great  sensitiveness  and   refinement,  reading 
direct  to  hundredths  of  a  degree.     Because  of  an  exceptionally  large 
bulb,  the  degree  divisions  are  very  long,  allowing  of  very  fine  sub- 
division.   With  such  a  thermometer  one-tenth  of  i°  C.  is  a  large 
amount.    The  accompanying  illustration  should  make  the  scheme  of 
the  apparatus  clear,  and  it  will  be  seen  that  it  is  a  simple  one  to  get 
up  in  the  laboratory  for  actual  work,  the  thermometer  being  the  only 
costly  element.     For  exceedingly  accurate  research  work  thermom- 
eters may  be  had  reading  to  thousandths  of  a  degree.     There  are 
also  metallic  thermometers  with  which  temperatures  are  measured  by 
the  change  in  electrical  resistance  of  a  little  coil  of  platinum  wire, 
and  the  delicacy  is  almost  without  limit.     For  all  practical  purposes, 
however,  a  mercury  thermometer  reading  to  hundredths  meets  every 
requirement.     The  practical  carrying  out  of  an  experiment  with 
such  a  Beckmann  apparatus  as  shown  in  Fig.   14  is  as   follows: 
An  accurately  weighed  quantity  of  pure  distilled  water  is  introduced 


34 


EXPERIMENTAL   ELECTROCHEMISTRY. 


in  the  tube  A,  which  in  turn  is  placed  in  the  tube  B  and  packed 
around  with  a  mixture  of  ice  and  salt.  The  large  tube  B  provides 
an  air-space  around  the  tube  A,  and  causes  a  more  uniform  freezing 


B 


FIG.  14. 

FIG.  14. — Form  of  Beckmann's  Apparatus  for  the  Study  of  Electrolytes  and  Non-elec- 
trolytes by  Depression  of  Freezing-points.  A,  large  glass  test-tube  with  side  neck; 
B,  larger  glass  tube  with  cork  to  receive  test-tube;  C,  large  glass  jar  to  receive 
both  tubes  and  freezing-mixture;  D,  stirrer;  EE,  wire  stirrers  within  test-tube; 
G,  side  neck  into  which  the  substance  to  be  tested  is  placed;  F,  delicate  "open- 
scale"  thermometer. 

FlG.  15. — Apparatus  for  Experimentally  Determining  the  Elevation  of  Boiling-points 
of  Electrolytes  and  Non-electrolytes.  A,  flask  with  double  side  necks;  B,  asbes- 
tos ring  supporting  flask  on  tripod;  C,  little  cylinder  of  platinum  within  flask 
to  prevent  cooled  condensed  water  from  striking  the  thermometer-bulb;  D,  Bun- 
sen  burner;  E,  condenser  with  water-jacket;  F,  Beckmann  thermometer  with 
mercury-reservoir  at  top;  G,  enlarged  view  of  mercury  reservoir. 

of  the  water  in  the  inner  tube.  The  air  between  the  two  tubes  becomes 
chilled  below  the  freezing-point  of  pure  water  and  freezes  the  water 
in  the  inner  tube.  The  stirrer  E  is  moved  up  and  down  in  the  dis- 


THE  THEORY  OF  ELECTROLYTIC   DISSOCIATION.  35 

tilled  water,  and  the  thermometer  is  carefully  watched.  The  mer- 
cury will  fall  steadily  until  the  sudden  formation  of  flakes  of  ice 
throughout  the  water  occur,  when  it  will  quickly  rise  a  little  and 
remain  stationary,  and  this  reading  should  at  once  be  taken.  With, 
a  correct  thermometer,  the  indication  should  of  course  be  o°  C_ 
If  the  reading  is  not  exactly  o°  it  matters  not,  so  long  as  we  are 
merely  measuring  the  differences  between  the  freezing-point  of  pure 
water  and  water  containing  compounds  in  solution.  At  least  three 
readings  should  be  made  with  the  same  water,  allowing  the  ice  to 
melt  and  then  freezing  over  again,  and  taking  the  average  of  the 
three  temperatures  for  the  freezing-point  of  the  pure  solvent.  The 
sudden  rise  of  the  thermometer  is  due  to  a  small  supercooling  of  the 
water  (in  spite  of  the  fact  of  its  being  stirred),  below  its  freezing-point, 
and  then  its  warming  up  again  at  the  instant  of  the  formation  of  ice 
It  is  well  known  to  those  who  have  studied  physics  that  water  throws 
off  heat  when  it  freezes,  the  phenomenon  being  attributed  to  latent 
heat.  Having  determined  carefully  the  experimental  freezing-point  of 
the  water,  a  carefully  weighed  quantity  of  the  substances  to  be  tested  is 
introduced  through  the  side  tube  D  and  allowed  to  dissolve.  The  freez- 
ing process  is  then  repeated  three  times,  as  with  pure  water,  and  the 
average  of  the  three  readings  is  taken.  If  the  water  and  compound 
have  been  so  weighed  as  to  give  a  normal  solution,  and  the  com- 
pound is  a  non-electrolyte,  we  will  obtain  the  figure  1.86°,  working,, 
of  course,  with  a  centigrade  thermometer.  The  important  point  to> 
observe  in  making  all  these  freezing-point  determinations  is  to  read 
the  thermometer  at  once  after  the  sudden  rise  of  the  thermome- 
ter, at  the  time  of  the  formation  of  the  ice.  If  we  wait,  and  keep  on* 
with  the  freezing  process,  the  thermometer  will  fall  again,  due  to  the 
fact  that  the  solution  has  become  concentrated  by  the  freezing  out 
of  some  of  the  water.  This,  of  course,  concentrates  the  solution 
and  gives  it  a  new  and  lower  freezing-point.  Electrolytes  are  treated. 
in  the  same  manner  as  non-electrolytes.  There  is  another  method 
which  we  should  not  pass  over  without  notice,  and  that  is  the  testing: 
of  electrolytes  and  non-electrolytes  by  the  elevation  of  the  boiling- 
point.  It  is  well  known  that  pure  water  boils  at  a  constant  tempera- 
ture under  a  constant  atmospheric  pressure,  and  that  the  heights 
of  mountains  have  been  measured  by  the  decrease  in  boiling-point 
of  water  with  a  delicate  thermometer.  It  is  also  very  well  known. 


36  EXPERIMENTAL   ELECTROCHEMISTRY. 

that  the  presence  of  dissolved  substances  increases  the  boiling-point 
of  pure  water.  Raoult  also  investigated  this  phenomenon  experi- 
mentally, and  found  that  normal  solutions  of  non-electrolytes  increased 
the  temperature  of  the  boiling-point  to  the  same  extent.  He  also 
.showed  that  all  electrolytes  of  comparable  concentration  elevated 
the  boiling-point  to  a  much  greater  extent.  Fig.  15  illustrates  a  piece 
of  apparatus  for  experimentally  determining  the  elevation  of  boiling- 
points  with  great  accuracy.  This  special  type  of  thermometer  has  an 
arbitrary  scale,  that  is,  it  is  not  designed  to  indicate  absolute  tempera- 
lures,  but  only  differences  between  temperatures.  The  little  reser- 
voir at  the  top  contains  a  supply  of  mercury,  which  may  be  shaken 
down  to  join  on  to  the  column  within  the  bore,  thus  allowing  the  instru- 
ment to  be  used  with  liquids  of  lower  boiling-points.  There  are  only 
.about  eight  degree  divisions  upon  the  entire  scale  of  such  a  delicate 
instrument,  and  were  it  not  for  the  flexible  character  due  to  the 
mercury-reservoir,  the  use  of  such  a  thermometer  would  be  exceed- 
ingly limited.  With  a  set  of  two  such  instruments,  one  designed  for 
low  temperatures  and  the  other  for  high  temperatures,  in  view  of  the 
little  reservoirs,  we  are  equipped  for  experimental  work  throughout 
a  very  wide  range.  With  either  thermometer  we  may  take  from  the 
reservoir,  or  return  to  the  reservoir,  by  shaking  the  instrument, 
thereby  making  it  serviceable  for  use  at  almost  any  temperature. 
In  conducting  experiments  with  this  apparatus,  a  few  fragments  of 
broken  glass  are  introduced  in  the  flask  to  prevent  "bumping" 
when  the  solution  boils.  We  see,  therefore,  from  these  two  experi- 
mental investigations  of  Raoult,  that  we  have  the  most  excellent 
evidence  in  favor  of  the  theory  of  electrolytic  dissociation. 

ADDITIONAL  EVIDENCE.      THE  NEUTRALIZATION  OF  ACIDS  AND  BASES. 

One  of  the  commonest  and  most  familiar  chemical  reactions  is 
the  neutralization  of  an  acid  by  a  base  with  the  formation  of  a  salt 
and  water.  The  following  is  a  simple  example,  where  hydrochloric 
acid  and  sodium  hydroxide  are  brought  together  in  solution: 

HCl+NaOH  = 


Here  we  have  sodium  chloride  (common  salt)  and  water  formed 
in  the  reaction.  So  much  for  the  general  chemistry  of  the  reaction. 
We  also  have  a  physical  side  to  the  reaction,  and  this  concerns  the 


THE   THEORY   OF   ELECTROLYTIC   DISSOCIATION. 


37 


heat  produced  when  the  reaction  takes  place.  The  general  chemist 
has  to  do  with  the  products  formed,  and  the  physical  chemist  has 
to  do  with  the  energy  transformations  and  their  measurement. 
Now  in  the  above  reaction  heat  is  liberated,  and  it  remains  for  us. 


Gli 


«A 


FIG.  1 6. — Calorimeter  for  Measuring  the  Heat  Liberated  when  Solutions  of  Electro- 
lytes are  Mixed  together  and  Allowed  to  React.  A ,  brass  calorimeter-casing  con- 
taining mass  of  water,  B.  There  is  also  an  inner  calorimeter-casing  of  polished 
metal,  C,  and  the  reaction-chamber,  D;  E,  hair-felt  covering;  F,  stirrer;  G, 
glass  reservoir  with  stopcock;  H  and  7,  two  similar  thermometers  of  sensitive 
type  reading  to  hundredths  of  a  degree;  /,  thermometer  indicating  temperature 
of  water-jacket;  K,  wooden  wedges  to  insulate  calorimeter. 

to  determine  how  much,  and  see  if  it  has  anything  to  do  with  our 
theory  of  electrolytic  dissociation.  Let  us  carry  on  such  a  chem- 
ical reaction  and  experimentally  measure  the  amount  of  heat  given 
out.  For  this  purpose  we  shall  require  a  calorimeter  like  that 
represented  in  Fig.  16.  It  is  easily  made  of  polished  brass  by  any-' 


38          EXPERIMENTAL  ELECTROCHEMISTRY. 

.good  sheet-metal  worker,  and  is  a  valuable  piece  of  apparatus  for 
the  physical-chemical  laboratory.  The  inner  reaction-chamber  D 
should  be  of  thin  platinum,  however.  For  our  experiment  we  will 
place  a  normal  solution  of  sodium  hydroxide  within  the  platinum 
chamber,  and  a  normal  solution  of  hydrocholoric  acid  within  the 
glass  reservoir  with  the  stopcock  turned  off.  The  two  thermom- 
eters are  inserted,  and  the  entire  apparatus  is  allowed  to  stand  for 
a  sufficiently  long  time  to  allow  equilibrium  to  be  established.  The 
thermometers  are  then  read,  and  the  hydrochloric  acid  from  the 
reservoir  is  allowed  to  run  into  the  calorimeter  while  the  stirrer  F 
is  operated.  The  thermometer  I  is  carefully  watched  until  the 
mercury  rises  to  the  highest  point.  Now  we  are  to  measure  the 
teat  of  the  reaction  in  calories,  and  in  order  to  do  this  it  is  only 
necessary  to  know  the  mass  of  the  liquid  raised  through  the  indi- 
cated temperature,  and  to  make  the  usual  calorimetric  corrections. 
We  must  know  and  allow  for  the  specific  heat  of  the  mixture,  the 
weight  and  specific  heat  of  the  platinum  vessel,  the  heat  exchange 
of  the  calorimeter,  etc.  The  detailed  method  of  working  with 
calorimeters  can  be  found  in  any  good  laboratory  treatise  on  gen- 
eral physics.  As  a  result  of  such  an  experiment  with  hydrochloric 
acid  and  sodium  hydroxide  we  get  13,700  calories,  in  addition  to 
the  formation  of  the  salt  and  the  water.  Now  to  come  to  the  point; 
It  matters  not  what  acid  and  what  base  we  use,  or  what  salt  is  formed, 
we  always  get  experimentally  in  such  a  calorimeter  determination 
13,700  calories.  The  following  table  indicates  the  run  of  things, 
and  it  now  remains  for  us  to  interpret  the  meaning  and  see  what 
it  has  to  do  with  electrolytic  dissociation.  The  first  table  gives  a 
varying  acid  and  a  constant  base,  and  the  second  table  a  varying 
base  and  a  constant  acid. 

HCl  +  NaOH  liberates  13,700  calories. 

HBr  +  NaOH  liberates  13,700  calories. 

HI  +  NaOH  liberates  13,700  calories. 

HNO3  +  NaOH  liberates  13,700  calories. 

HCl-f  LiOH  liberates  13,700  calories. 
HCl-f  KOH  liberates  13,700  calories. 
HCl+"Ba(OH)2  liberates  13,800  calories. 
HCl  +  Ca(OH)2  liberates  13,900  calories. 


THE  THEORY  OF  ELECTROLYTIC  DISSOCIATION.  39 

In  the  case  of  the  calcium  and  barium  hydroxides,  one-half 
normal  solutions  were  taken  to  normal  solutions  of  hydrochloric 
acid,  for  the  reason  that  calcium  and  barium  are  bivalent.  The 
above  tables  exhibit  to  us  a  remarkable  performance,  and  it  re- 
mains for  the  physical  chemist  to  explain  it.  The  theory  of  electro- 
lytic dissociation  explains  it  perfectly,  and  in  so  doing  gains  im- 
portant experimental  evidence  in  its  own  support. 

HC1  and  NaOH  react  and  give  NaCl  and  H2O. 

In  terms  of  our  theory,  however,  these  bodies  would  be  disso- 
ciated and  represented  thus: 

+    -  +  +     - 

H  Cl  and  Na  OH  react  and  give  Na  Cl  and  H2O. 

Salt  and  water  are  the  products,  of  course,  but  as  the  salt  is 

+     - 
born  in  water,  so  to  speak,  it  is  dissociated  as  represented  as  Na  Cl, 

and  not  as  NaCl,  as  it  would  be  out  of  solution.  The  only 
thing  really  formed  in  the  molecular  state  is  water,  and  the  constant 
of  13,700  calories  is  merely  the  heat  of  formation  of  water.  All 
bodies  have  either  a  positive  or  a  negative  heat  of  formation,  and 
if  the  salt  is  formed  in  the  molecular  condition  along  with  the  water, 
it  would,  of  course,  add  its  own  heat  of  formation  to  the  sum  total, 
and  as  different  salts  have  different  heats  of  formation,  we  would, 
of  course,  not  get  a  constant,  but  a  different  number  of  calories  for 
each  reaction  between  an  acid  and  a  base.  The  following  table 
gives  the  heats  of  formation  of  a  number  of  salts  produced  by  the 
acids  and  bases  which  we  have  tabulated: 

NaCl 9,760  calories. 

NaBr 8,580  calories. 

Nal 6,910  calories. 

NaNO3 11,130  calories. 

LiCl 9,380  calories. 

KC1 10,430  calories. 

BaCU *9,47o  calories. 

CaCl2 16,980  calories. 

In  the  case  of  the  calcium  and  barium  chlorides,  one-half  the 
indicated  number  of  calories  must  be  taken,  for  the  reason  that  cal- 


40  EXPERIMENTAL   ELECTROCHEMISTRY. 

cium  and  barium  are  bivalent  and  require  double  the  quantity  of 
acid. 

It  will  thus  be  seen  that  without  the  theory  of  electrolytic  dis- 
sociation we  would  be  unable  to  explain  the  liberation  of  a  con- 
stant number  of  calories,  when  an  acid  reacts  with  a  base. 

ADDITIONAL   EVIDENCE. 

Let  us  take  four  electrolytes,  for  example,  and  make  two  mix- 
tures. For  this  purpose  we  will  choose: 


First  mixture:       Potassium  nitrate, 

Sodium  iodide,       Nal. 

Second  mixture:  Potassium  iodide,  KI; 

Sodium  nitrate,      NaNOs. 

Dilute  solutions  of  both  salts  in  each  mixture  are  represented 
as  follows,  with  all  the  constituents  dissociated: 

K     NO3     and     Na     I; 
K    I     and     Na    NO3. 

In  terms  of  the  theory  of  electrolytic  dissociation  we  have  ex- 
actly the  same  ions  present  in  both  cases,  and  the  properties  of  the 
two  mixtures  should  be  absolutely  the  same.  The  two  solutions, 
when  equivalent  quantities  of  the  different  substances  are  taken, 
are  found  to  be  identical  in  every  respect. 

FURTHER     EVIDENCE.      EXPERIMENTS      WITH     PERFECTLY     DRY 

COMPOUNDS. 

Let  us  take  any  of  the  "  chemically  active"  bodies,  or  electrolytes, 
and  inquire  into  their  behavior  when  perfectly  dry.  In  terms  of 
the  theory  of  electrolytic  dissociation,  dry  electrolytes  are  in  the 
molecular  condition  and  are  also  "  chemically  inactive."  In  terms 
of  the  theory,  the  dissociation  products,  or  ions  alone,  are  capable 
of  entering  into  chemical  combinations.  Let  us  test  this  matter 
carefully  by  referring  to  a  number  of  experiments  involving  the 
careful  drying  of  the  substances  employed.  It  is  well  known  to 


THE   THEORY   OF   ELECTROLYTIC  DISSOCIATION.  41 

chemistry  that  ammonia  gas,  NH3,  and  hydrochloric-acid  gas,  HC1, 
react  at  once  to  form  ammonium  chloride,  NKUCl: 

NH3  +  HC1  =  NH4C1. 

The  white  clouds  of  ammonium  chloride  are  even  manifested 
when  an  ammonia  bottle  is  unstoppered  in  the  neighborhood  of 
hydrochloric  acid.  It  has  been  shown  by  the  most  careful  and 
patient  workers  that  thoroughly  dry  ammonia  gas  and  thoroughly 
dry  hydrochloric-acid  gas  do  not  react  to  form  ammonium  chloride, 
and  may  be  separated  after  mixing  in  a  thoroughly  dry  receiver. 
The  accompanying  illustrations  show  how  this  may  be  accom- 
plished after  the  gases  have  been  produced  and  thoroughly  dried. 
The  absolute  drying  of  these  gases  is  a  difficult  and  tedious  process, 


FlG.  17. — Diagram  Representing  an  Uncombined  Mixture  of  Dry  Ammonia  Gas  and 
Dry  Hydrochloric  Acid  Gas.  The  respective  gases  are  here  being  separated  by 
charged  electrodes,  where  they  may  be  drawn  off  and  tested. 

for  the  slightest  trace  of  moisture  in  either  the  gases  or  the  glass- 
globe  will  defeat  the  object  of  the  experiment.  They  may,  of  course, 
be  dried  by  passing  through  towers  of  finely  broken  lime  and  phos- 
phorous pentoxide.  The  globe  must  be  heated  to  a  high  tempera- 
ture by  means  of  a  Bunsen  flame,  while  thoroughly  dried  air  is 
passed  through.  In  every  detail  the  most  elaborate  precautions 
must  be  taken  against  having  moisture  present.  In  this  case  we 
have  two  molecules,  NH3  and  HC1,  behaving  like  ions,  that  is,  the 
one  goes  to  the  positive  pole  and  the  other  to  the  negative  pole. 
The  student  may  ask  how  it  is  that  we  have  hydrogen  going 
to  the  positive  pole,  as  in  the  HC1  diagrammatically  represented 
within  the  globe  in  Fig.  17.  If  he  will  turn  to  the  first  chapter  and 
examine  the  elements  arranged  in  their  " electrochemical  order," 


42 


EXPERIMENTAL  ELECTROCHEMISTRY. 


he  will  note  that  chlorine  is  much  more  strongly  electronegative 
than  hydrogen  is  electropositive,  and  being  linked  to  the  hydrogen, 
draws  it  to  the  positive  pole.  In  the  case  of  ammonia,  we  may 
think  of  the  hydrogen  winning  and  dragging  the  nitrogen  to  the 
negative  pole,  because  there  are  three  hydrogen  atoms  to  the  one 


FIG.  18. — Glass  Globe  with  Electrodes  Leading  to  Static  Machine  for  Separating  a 
Perfectly  Dry  Mixture  of  Ammonia  and  Hydrochloric  Acid  Gases.  After  mix- 
ing together  in  the  globe  the  gases  may  be  separated  by  static  charges  upon  the 
electrodes  and  be  drawn  off  through  the  glass  tubes. 

of  nitrogen  in  the  ammonia  molecule.  Atom  for  atom  nitrogen  is 
more  strongly  electronegative  than  hydrogen  is  electropositive,  as 
can  be  readily  seen  from  the  table,  but  there  are  three  hydrogen 
atoms  pulling  the  one  nitrogen  atom,  and  we  may  compare  matters 
to  a  game  of  football  where  three  players  for  one  goal  get  hold  of 
a  single  player  for  the  other  goal.  The  single  player  is  pulling 
harder  than  any  one  of  the  others  to  make  his  goal  because  he  is 
stronger,  but  he  is  overpowered  in  number.  Fig.  18  shows  a  glass 
globe  on  an  electrical  machine  for  carrying  out  such  an  experiment. 


THE  THEORY  OF  ELECTROLYTIC  DISSOCIATION.  43 

So  much  for  this  experiment.  The  following  list  represents  work 
done  by  various  experimenters  in  support  of  the  dissociation  theory: 

Perfectly  dry  sulphuric  acid  has  been  shown  not  to  act  on  per- 
fectly dry  metallic  sodium! 

Dry  hydrocholric  acid  does  not  act  on  carbonates. 

Dry  hydrogen  and  chlorine  may  be  mixed  together  and  exposed 
to  the  sunlight  without  an  explosion  taking  place. 

Dry  hydrochloric-acid  gas  does  not  precipitate  silver  nitrate 
from  water-free  ether  or  benzene  solution. 

Dry  acids  will  not  act  upon  litmus  paper,  and  will  not  form 
salts  with  dry  bases. 

Absolutely  dry  oxygen  gas  will  not  support  combustion  in  many 
moisture-free  substances ! 

Dry  chlorine  does  not  combine  with  metals,  not  excepting  sodium 
and  potassium. 

Absolutely  dry  gunpowder  could  not  be  ignited!! 

Allow  the  slightest  trace  of  water  vapor  to  enter  the  field  in  any 
of  the  above  cases  and  we  have  immediate  reactions.  What  part 
does  the  water  play?  In  terms  of  our  theory  it  is  the  dissociant, 
or  cause  for  breaking  down  the  molecules.  Fig.  19  represents  a 
molecule  consisting  of  th  atoms  A  and  B,  with  the  "  chemical 
affinity"  between  them  assigned  to  electrical  attraction  of  unlike 
charges.  The  atoms  in  the  molecule  here  are  believed  to  be  held 
together  by  electrical  attraction.  Now  bring  such  a  molecule  into 
the  presence  of  water.  The  negative  atom  will  induce  a  positive 
charge  in  the  water,  and  the  positive  atom  will  induce  a  negative 
charge  in  the  water.  Now,  according  to  J.  J.  Thomson,  one  of 
England's  most  distinguished  and  famous  physicists,  because  of 
these  induced  charges  the  attraction  between  the  atoms  A  and  B 
will  be  weakened,  and  when  immersed  in  the  water  will  be  lost 
altogether.  The  following  are  Prof.  Thomson's  words  describing 
the  condition  when  such  a  molecule  as  represented  in  AB  in  the 
little  diagram  Fig.  20  is  brought  near  a  conducting  sphere:  "Thus 
let  AB  represent  two  atoms  in  a  molecule,  placed  near  a  conducting 
sphere,  then  the  effect  of  the  electricity  induced  on  the  sphere  by 
A  will  be  represented  by  an  opposite  charge  A',  the  image  of  A  in 
the  sphere.  If  A  is  very  near  the  surface  of  the  sphere,  then  the 
negative  charge  at  A'  will  be  very  nearly  equal  to  that  of  A.  Thus 


44 


EXPERIMENTAL   ELECTROCHEMISTRY. 


the  effect  of  the  sphere  will  be  practically  to  neutralize  the  effects  of 
A ;  as  one  of  these  effects  is  to  hold  the  atom  B  in  combination,  the 
affinity  between  the  atoms  A  and  B  will  be  almost  annulled  by 
the  presence  of  the  sphere.  Molecules  condensed  on  the  surface 
of  the  sphere  will  thus  be  practically  dissociated.  The  same  effect 
would  be  produced  if  the  molecules  were  surrounded  by  a  substance 
possessing  a  very  large  specific  inductive  capacity.  Since  water 


r*  i-» 

0   © 


FIG.  19.  FIG.  20. 

FiG.  19. — Diagram  Illustrating  the  Part  Played  by  a  Dissociant  when  an  Electrolyte 
is  Immersed.  A  and  B  are  the  atoms  of  a  molecule. 

FiG.  20. — Diagram  Illustrating  Prof.  J.  J.  Thomson's  Theory  of  Electrolytic  Disso- 
ciation, assuming  that  the  atoms  in  a  molecule  are  held  together  by  electrical 
attraction. 

is  such  a  substance,  it  follows,  if  we  accept  the  view  that  the  forces 
between  the  atoms  are  electrical  in  their  origin,  that  when  the  mole- 
cules of  a  substance  are  in  aqueous  solution  the  forces  between 
them  are  very  much  less  than  they  are  when  the  molecule  is  free 
and  in  a  gaseous  state." 

Thus  far  we  have  considered  only  solutions  of  electrolytes  in 
water.  Water  has  therefore  been  the  dissociant  in  all  the  cases 
which  we  have  so  far  met  with.  Although  water  is  the  strongest 
dissociant  known,  there  are  other  liquids  capable  of  breaking  down 
molecules  when  solutions  are  made  in  them.  By  strongest  dissociant 
known  we  mean  a  solvent  which  breaks  the  largest  number  of  mole- 
cules down  into  ions  per  unit  of  solvent  volume.  In  very  concen- 


THE  THEORY   OF   ELECTROLYTIC   DISSOCIATION.  45 

trated  solutions  of  electrolytes  we  have  a  mixture  of  molecules  and 
ions.  As  the  dilution  is  increased  the  number  of  ions  increases, 
for  upon  the  addition  of  more  water  more  of  the  molecules  are  broken 
down.  The  strong  acids,  bases,  and  salts  are  completely  dissociated 
when  a  molugram  equivalent  is  dissolved  in  1000  liters  of  water. 
If  we  dissolve  a  molugram  of  a  strong  acid  in  500  liters  of  water, 
we  will  have  in  solution  molecules  and  ions.  The  solution  con- 
ducts the  electric  current  solely  by  the  transport  of  the  electricity 
by  the  free  ions.  If  we  measure  the  conductivity  of  such  a  solu- 
tion, we  will,  of  course,  obtain  a  certain  conducting  value.  Now, 
what  will  be  the  effect  of  diluting  the  solution  with  water?  With 
further  dilution  we  get  increased  ionization  up  to  the  point  where 
there  are  no  molecules  left,  all  having  broken  down  into  ions  We 
should  expect  the  molecular  conductivity  of  the  solution  to  increase 
upon  diluting  with  water,  if  the  dissociation  theory  is  true.  As  a 
matter  of  fact,  the  molecular  conductivity  does  increase  up  to  the 
point  where  we  have  a  gram-molecular  equivalent  dissolved  in  1000 
liters  of  water.  Now,  water  being  the  strongest  dissociant  known, 
all  other  solvents  must  be  present  in  larger  quantity  to  effect  an 
equal  dissociation.  We  will  now  give  a  table  with  the  dissocia'nts 
in  order  of  their  strength,  and  follow  it  by  an  easily  performed  prac- 
tical experiment  to  show  that  dissociation  increases  upon  dilution. 

DISSOCIANTS   IN   ORDER   OF   POWER. 

Water. 
Formic  acid. 
Methyl  alcohol. 
Ethyl  alcohol. 

There  are  other  dissociants,  but  the  above  are  among  the  most 
common  and  generally  employed.  J.  J.  Thomson  has  also  shown 
that  the  dissociating  power  bears  a  relation  to  the  dielectric  constants. 
This  is  in  support  of  the  theory  of  the  electrical  attraction  between 
the  atoms  in  a  molecule.  Having  stated  that  dissociation  and 
electrical  conductivity  increase  upon  dilution  up  to  a  point  where 
we  have  the  gram-molecule  dissolved  in  1000  liters  of  water, 
we  will  now  test  it  by  experiment. 


46  EXPERIMENTAL   ELECTROCHEMISTRY. 

PRACTICAL    EXPERIMENT    TO    SHOW   DISSOCIATION    AND    INCREASE    IN 
ELECTRICAL    CONDUCTIVITY    UPON    DILUTION   WITH    WATER. 

In  the  following  experiment  there  is  developed  a  double  and 
simultaneous  indication  of  ionization,  the  appearance  of  a  deep- 
red  color  on  the  one  hand  and  the  steady  increase  of  electrical 
conductivity,  upon  the  addition  of  water,  on  the  other  hand.  The 
color  change  is  dependent  upon  the  well-known  behavior  of  phenol- 
phthalein  as  a  chemical  indicator.  To  the  characteristic  color 
deportment  of  this  interesting  compound  the  conductivity  method 
is  simultaneously  applied.  The  experiment  as  heretofore  exhibitel 
consists  in  merely  noting  the  color  change  which  is  produced  as 
follows:  A  small  quantity  of  phenolphthalein  is  dissolved  in  ethyl 
alcohol  and  is  poured  into  a  tall  glass  lecture-jar  to  a  height  of  about 
5  centimeters.  A  few  drops  of  ammonia  water  are  then  carefully 
added.  There  will  be  a  slight  momentary  yellow  coloration,  which 
will  immediately  disappear  upon  shaking  if  too  much  ammonia 
water  has  not  been  added;  if  too  much  ammonia  water  has 
been  added,  add  more  alcohol.  Now,  chemists  know  that  a 
colorless  solution  of  phenolphthalein  turns  a  beautiful  red  in  the 
presence  of  a  base.  Here  we  have  the  phenolphthalein  and  the 
base,  ammonium  hydroxide,  in  alcoholic  solution  together,  and  no 

red    color    appears.     Why?     Ammonium    hydroxide    cannot    show 

+ 
its  basic  properties  until  dissociated  into  the  ions  NH4,  OH,  the 

isolated  OH  or  hydroxyl  producing  such  basic  manifestations. 
Now,  if  we  look  at  the  table  of  dissociants,  we  see  that  ethyl  alcohol 
is  a  very  poor  dissociant  and  is  unable  to  break  the  ammonium- 
hydroxide  molecules  down  into  ions.  Now,  what  will  happen  if 
we  add  some  water?  Water,  as  will  be  seen  from  the  table,  heads 
the  list  as  the  strongest  dissociant  known,  and  we  should  expect  it 
to  ionize  the  ammonium-hydroxide  molecules  if  it  be  added.  If 
the  ammonium-hydroxide  molecules  are  dissociated  or  ionized, 
we  should  expect  the  red  color  of  the  phenolphthalein  to  appear 
and  become  deeper  and  deeper  as  the  molecules  are  broken  up 
into  active  ions.  This  is  just  what  happens.  Upon  the  addition 
of  water  the  color  begins  to  appear  and  continues  to  get  deeper 
and  more  decided  as  dilution  continues.  This  is  an  odd  sight,  to 
see  the  addition  of  pure  water  to  a  faintly  colored  solution  produce 


THE   THEORY   OF  ELECTROLYTIC   DISSOCIATION. 


47 


a  deeper  and  deeper  color  as  dilution  goes  on.     So  much  for  the 
color  indication  of  dissociation  on  dilution.     Now,   molecules  do 


not  conduct  the  electric  current,  and  it  occurred  to  the  author  to 
perform  this  same  experiment  over  again,  but,  instead  of  using  the 


48  EXPERIMENTAL  ELECTROCHEMISTRY. 

glass  jar,  to  employ  a  glass  tank  provided  with  electrodes  and  study 
the  conductivity  behavior  at  the  instant  the  color  appears  and  follow 
the  conductivity  behavior  as  the  phenolphthalein  deepens  in  color. 
Tor  this  purpose  a  piece  of  apparatus  was  made  as  illustrated  in 
Fig.  21.  With  such  a  piece  of  apparatus  we  should  not  only  ob- 
tain the  color  reaction  with  an  indicator,  but  an  increasing  con- 
ductivity of  the  solution.  The  experiment  is  best  and  most  forcibly 
shown  by  first  filling  the  tank  with  pure  distilled  water  to  the  top, 
having  washed  it  out  many  times  previously  with  distilled  water  to  get 
it  perfectly  clean,  when  there  will  be  practically  no  indication  upon  the 
galvanometer.  The  water  is  next  poured  out  and  the  tank  carefully 
drained  and  dried  as  much  as  possible.  It  is  then  filled  to  the  same 
level  with  a  solution  of  phenolphthalein  in  ethyl  alcohol  to  which 
some  ammonium  hydroxide  solution  has  been  added.  This  should 
be  colorless,  as  will  be  the  case  if  not  too  much  ammonia  was  added. 
There  will  be  practically  no  indication  upon  the  galvanometer.  We 
have  then  separately  tested  the  conductivity  of  the  water  and  the 
solution.  Let  us  now  see  what  the  addition  of  water  accomplishes. 
For  this  phase  of  the  experiment  the  phenolphthalein  solution  is 
poured  out,  all  but  a  small  quantity.  The  writer  usually  leaves 
solution  in  the  bottom  to  a  depth  of  about  5  centimeters.  Water 
is  now  very  slowly  added,  when  the  red  color  begins  to  appear,  and  at 
the  same  instant  the  galvanometer  begins  to  show  conductivity.  As 
the  red  color  increases  the  electrical  conductivity  also  increases,  as 
is  plainly  shown  by  the  galvanometer.  The  dilution  is  continued 
until  the  tank  is  full.  The  tank  is  constructed  with  a  distance 
between  the  glass  sides  of  only  i  centimeter,  and  therefore  requires 
but  a  small  volume  of  solution.  The  joint  between  the  glass  and 
the  wood  is  made*  in  a  deep  groove  by  cement.  We  will  now  close 
the  present  chapter  with  definitions  of  the  new  terms  introduced. 

Gram-molecule,  or  molugram. — Molecular  weight  of  a  compound 
expressed  in  grams.  The  molecular  weight  of  sodium  chloride  is 
58.5.  In  order  to  use  a  gram-molecule  of  sodium  chloride  we 
would  weigh  out  58.5  grams  of  the  substance,  for  example. 

Latent  heat. — The  amount  of  heat  required  to  change  the  phys- 
ical state  of  a  body  without  changing  its  temperature.  The  heat 
given  out  or  absorbed  when  certain  bodies  change  their  physical 
states. 


NOVEL   EXPERIMENTS   IN   "ELECTROLYTIC   INDUCTION."      55 

Force  of  Platinum  in  Contact  with  Acidulated  or  Alkalinized  Water: 
Two  plates  of  platinum  were  immersed  in  acidulated  water  for 
some  time.  One  being  withdrawn,  washed  in  distilled  water,  and 
returned,  was  found  to  be  negative.  Electromotive  force  =  0.0136 
volt.  Water  alkalinized  with  KOH  was  then  substituted.  The 
washed  and  returned  plate  was  found  to  be  positive.  Identical 
results  were  obtained  with  plates  of  platinized  platinum.  It  is 
possible  to  recognize  by  this  means  whether  a  liquid  is  neutral,  or 
acid  or  alkaline,  even  when  its  reaction  is  so  feeble  as  not  to  affect 
test-papers." 

Now  the  author's  experiment  consists  in  operating  the  electrical 
machine,  when  the  tinfoil  coating  of  the  beaker  B  will  be  positively 

charged  and  will  hold  the  negative  ions  of  the  potassium  chloride 

+    - 

K  Cl,  which,  as  may  be  readily  seen,  are  chlorine  ions,  and  will  repel 

the  positive  ions  which  are  potassium  through  the  moist  cord  into  the 
beaker  C,  where  they  may  be  discharged,  after  the  removal  of  the  wet 
cord,  bv  the  platinum  wire  shown  at  the  right  of  the  beaker  Upon 
discharging  the  potassium  ions  they  become  potassium  atoms  and 
react  with  the  water  as  before  2K  +  2H2O  =  2KOH  +  H2,  forming 
potassium  hydroxide  and  setting  hydrogen  free.  This  experiment  does 
not  attempt  to  show  migration  by  the*  setting  Tree  of  the  hydrogen, 
but  by  the  formation  of  the  alkali,  or  base,  KOH,  potassium  hydroxide. 
To  do  this  the  reflecting  galvanometer  is  employed.  It  would  be 
expected  that  the  chlorine  ions  could  be  discharged  in  the  same 
manner  and  their  presence  shown  by  a  drop  or  two  of  silver-nitrate 
solution.  Although  there  is  little  doubt  of  their  being  discharged  in 
the  same  manner,  the  minute  quantity  of  chlorine  present  would  not 
suffice  to  give  a  chemical  precipitation  of  silver  chloride.  Perhaps 
if  the  electrical  machine  was  allowed  to  run  for  several  days,  a  slight 
opalescence  might  be  observed  when  a  drop  or  two  of  silver  nitrate  is 
added.  When  we  complete  our  studies  of  Faraday's  law  involving 
the  electrochemical  equivalents  we  will  be  in  a  position  to  appreciate 
how  few  chlorine  ions  would  migrate  under  such  circumstances  as 
we  have  in  this  experiment.  All  ions  carry  very  great  electrical 
charges,  and  we  know  as  physicists  that  there  is  very  little  quantity 
of  electricity  to  be  had  from  a  static  machine.  The  electricity  from 
a  frictional  machine  is  almost  all  potential  difference!  The  amperage 
in  a  current  from  a  static  machine  is  so  small  as  to  be  detected  and 


EXPERIMENTAL   ELECTROCHEMISTRY. 


measured  only  by  very  special  means.  Now  a  few  ions  are  capable 
of  carrying  many  amperes,  as  we  shall  see  later,  and  it  is  not  sur- 
prising under  the  circumstances  that  our  static  charges  have  been 
carried  by  very  few  ions  indeed.  We  will  now  leave  experiments 
with  static  induction  and  study  the  effects  of  magnetic  and  galvanic 
induction  upon  electrolytes.  All  the  following  experiments  are 
based  upon  the  original  researches  of  the  present  author,  and  are 
now  published  for  the  first  time.  It  occurred  to  the  writer  to  com- 
pare electrolytes  with  metallic  conductors  when  under  the  influence 
of  magnets  and  electric  currents  in  neighboring  conductors,  to  see  if 
inductive  effects  and  inductive  currents  were  produced.  Will  a 
magnet  induce  a  current  of  electricity  in  an  electrolyte  as  it  does  in  a 
metallic  conductor  ?  This  question  is  not  touched  upon  in  the  treatises 
in  physics  or  chemistry,  and  it  was  therefore  resolved  to  answer  the 
question  by  experiment.  Fig.  25  shows  the  first  comparatively 


Q\ 


FIG.  25. — Experiment  to  Learn  the  Effect  of  a  Magnet  upon  a  Coil  of  Electrolyte. 
The  central  figure  represents  a  coil  of  wire  of  equal  resistance  and  dimensions, 
which  may  be  substituted  for  the  coil  of  electrolyte. 

rough  plan  for  learning  whether  a  magnet  will  induce  an  electric 
current  in  a  coil  of  electrolyte  as  it  does  in  a  coil  of  wire.  We  have 
here  a  sensitive  reflecting  galvanometer  at  the  right  to  show  any 
induced  current.  As  a  matter  of  fact  a  magnet  does  induce  a  current 
of  electricity  in  the  electrolyte  and  causes  the  galvanometer  to  indi- 
cate the  same.  The  coil  of  wire  represented  in  the  center  was  made 
of  equal  dimensions  with  and  substituted  for  the  coil  of  electrolyte 
to  ascertain  if  the  effect  was  quantitatively  the  same.  The  coil  of 


NOVEL   EXPERIMENTS   IN   "ELECTROLYTIC   INDUCTION."      51 


atoms  of  chlorine  and  potassium.  Imagine  two  insulated  vessels, 
B  and  C,  filled  with  a  solution  of  potassium  chloride  and  electrically 
connected  by  means  of  the  siphon  D.  Let  a  negatively  charged 
body  be  brought  near  B,  remove  the  siphon,  and  lastly  the  charged 
body  A  .  Then,  as  is  well  known,  B  remains  positively  electrified,  and 
C  negatively  .  electrified.  Now,  according  to  Faraday's  law,  the: 
electricity  in  electrolytes  can  only  move  simultaneously  with  the  ions.. 
Consequently,  if  an  excess  of  positive  electricity  is  present  in  B, 
there  must  also  be  an  excess  of  free  potassium  ions,  i.e.,  of  potassium 


B 


FIG.  22. — Prof.  Ostwald's  Experiment  in  Static  Induction  to  Show  the  Presence  of 
"  Free  Ions."  A,  negatively  charged  body;  B  and  C,  beakers  filled  with  a  solu- 
tion of  potassium  chloride;  D,  siphon-tube  filled  with  the  same  solution  and. 
joining  the  two  beakers. 

atoms,  by  the  electricity  of  which  the  charge  is  determined.  If  the 
electricity  is  conducted  away,  *  the  potassium  assumes  the  ordinary 
form,  and  acting  on  the  water  of  the  solution  develops  hydrogen, 
which  can  be  collected  in  suitable  apparatus  and  tested.  Similar 
considerations  hold  good  for  the  chlorine  in  the  vessel  C.  It  is 
consequently  not  only  conceivable  that  the  ions  in  an  electrolytic 
solution  move  about  with  electrical  charges,  otherwise  quite  free, 
but  solutions  may  be  prepared  which  contain  an  excess  of  any  ion 
we  choose,  e.g.,  an  excess  of  potassium.  The  assumption  that  elec- 
trolytes contain  free  ions  is  not  only  possible  but  necessary." 

This  experiment  as  originally  proposed  by  Ostwald  was  not  at  all 
practical,  for  the  quantity  of  hydrogen  gas  liberated  was  so  small  that 
it  could  not  be  seen.  The  liberation  of  hydrogen  is  based  upon  the 
following  simple  equation: 


*  By  inserting  in  the  beaker  B  a  platinum  wire  to  earth. — N.  M.  H. 


52  EXPERIMENTAL   ELECTROCHEMISTRY. 

The  experiment  was  eventually  modified  by  Profs.  Ostwald  and 
Nernst,  the  latter  being  also  one  of  the  most  brilliant  German  physical 
chemists  of  the  times.  This  experiment  shows  to  the  eye  the  libera- 
tion of  hydrogen  under  similar  conditions  of  static  induction,  and 
is  a  practical  illustration  of  great  beauty.  The  arrangement  of  the 
apparatus  for  this  experiment  is  shown  in  Fig.  23.  At  A  we  have 
the  positive  knob  of  a  static  electrical  machine  connected  by  a  tinsel 


FIG.  23. — Ostwald  and  Nernst's  Experiment  in  Static  Induction  to  Show  the  Pres- 
ence of  "  Free  Ions."  A,  positive  knob  of  electrical  machine;  B,  glass  flask  cov- 
ered with  tinfoil;  C,  wet  strings  connecting  the  glass  flask  and  the  vessel  D,  both 
containing  dilute  sulphuric  acid;  E,  burette  drawn  out  into  a  fine  capillary,  G, 
through  the  side  of  which  the  platinum  wire,  F,  is  fused;  H,  glass  plate  on  glass 
insulators. 

•cord  or  small  metal  chain  to  the  little  hook  on  the  tinfoil  covering 
of  the  glass  flask  B.  This  flask  is  filled  with  dilute  sulphuric  acid 
and  is  thoroughly  insulated  upon  a  glass  or  hard  rubber-plate  resting 
upon  small  insulators  also  of  glass.  Cords  or  strings  wet  with  the 
same  dilute  sulphuric  acid  dip  into  the  flask  and  connect  with  the 
vessel  D  also  containing  some  of  the  same  sulphuric-acid  solution, 
and  being  insulated  in  a  similar  manner.  The  glass  burettte  E  has 
been  drawn  out  into  a  long  and  fine  capillary  G  through  which  a 
fine  platinum  wire  is  fused  and  which  turns  to  earth.  Now  what 
happens  when  the  electrical  machine  is  put  into  operation  ?  The 


NOVEL   EXPERIMENTS   IN   "ELECTROLYTIC  INDUCTION."      53 

tinfoil  coating  being  electrically  connected  with  the  electrical 
machine  becomes  positively  charged,  which,  acting  through  the  glass 
of  the  flask,  attracts  and  holds  a  corresponding  amount  of  negative 
electricity,  while  the  positive  is  repelled.  The  positive  electricity, 

or,  as  we  believe,  the  positive  ions,  which  in  this  case  are  hydrogen. 

+     - 
(H2SO4  ionizes  into  H2  804)  is  repelled  through  the  moist  cord  which 

leads  to  the  vessel  D  and  the  capillary  of  the  burette  filled  with  the 
acid  and  water  to  a  height  of  a  few  centimeters,  when  it  meets  with 
a  little  column  of  mercury  at  G  connected  to  earth.  This  mercury 
was  drawn  up  into  the  capillary  by  placing  it  in  the  bottom  of  the 
vessel  D,  when  some  of  the  dilute  sulphuric-acid  solution  was  allowed 
to  follow.  Now  the  hydrogen  ions  are  repelled  through  this  system, 
and  are  discharged  when  they  reach  the  grounded  mercury.  They 
then  become  ordinary  atoms  of  hydrogen,  and  may  readily  be  seen 
in  the  capillary.  On  starting  the  electrical  machine  the  experimenters 
observed  a  rush  of  tiny  bubbles  of  gas  through  the  mercury  at  Gr 

collecting  at  the  top  under  the  glass  stop-cock,  the  SO 4  ion  being 
held  by  the  positive  attraction  on  the  outside  of  the  flask  B.  Here 
we  have  a  very  beautiful  experiment  based  upon  an  induction  phe- 
nomenon. The  experimenters  also  conducted  a  most  elaborate 
quantitative  research  upon  this  phenomenon,  to  ascertain  if  the 
amount  of  hydrogen  set  free  at  G  corresponded  to  that  calculated 
from  Faraday's  law,  and  found  within  the  limits  of  experimental 
error  that  it  did.  We  shall  take  up  Faraday's  law  and  the 
subject  of  electrochemical  equivalents  in  a  later  chapter,  but  at  the 
present  time  it  is  only  wise  to  state  that  all  ions  have  definite  capac- 
ities for  the  electrical  charges  according  to  their  valencies.  Knowing 
the  electrochemical  equivalent  of  hydrogen,  for  example,  it  would 
be  an  easy  matter  to  calculate  what  mass,  or  what  volume  of  hydrogen, 
would  be  set  free  by  a  given  quantity  of  electricity.  The  experi- 
menters referred  to  employed  such  a  course  in  checking  the  above 
experiment  quantitatively.  So  much  for  the  experiment  of  Ostwald 
and  Nernst,  depending  upon  the  liberation  of  hydrogen  as  proof  of 
the  migration  of  free  ions.  Fig.  24  illustrates  the  author's  modifi- 
cation of  this  experiment  based  upon  the  use  of  the  reflecting- 
galvanometer  as  a  chemical  indicator,  to  prove  that  ions  had  migrated 
under  the  influence  of  static  induction.  Gaugin,  and  later  Prof. 


54 


EXPERIMENTAL   ELECTROCHEMISTRY. 


Kuester,  employed  the  reflecting  galvanometer  as  a  chemical  indica- 
tor, and  the  use  of  such  an  instrument  for  detecting  acids  and  bases 


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be  described  before  we  describe  the  author's  experiment.     To 
quote  from  Gaugin's  work  we  have  the  following:    "Electromotive 


THE  THEORY  OF  ELECTROLYTIC   DISSOCIATION.  49 

Specific  heat. — The  amount  of  heat  required  to  raise  a  gram 
of  a  substance  one  degree  in  temperature  as  compared  with  the 
amount  of  heat  required  to  raise  one  gram  of  water  one  degree. 

Calorie. — The  unit  of  heat.  The  amount  of  heat  required 
to  raise  one  gram  of  water  one  degree  in  temperature.  There 
are  large  Calories  also,  being  icoo  times  the  small  calorie,  for  con- 
venience. 

H eat  exchange  oj  calorimeter. — Error  due  to  loss  of  heat  by  the 
calorimeter  itself,  by  radiation,  etc.  To  be  determined  by  experi- 
ment with  individual  calorimeters  by  blank  tests. 

Elevation  oj  boiling-point. — Often  expressed  in  works  on  phys- 
ical chemistry  as  "the  lowering  of  the  vapor-tension  of  the  solvent." 

"Bumping. " — The  liberation  of  steam  with  almost  explosive 
violence  from  the  smooth  interiors  of  glass  flasks  when  liquids  are 
boiled  in  them.  Prevented  by  introducing  sharp  points,  as  by 
the  introduction  of  broken  glass. 

Dissociant. — A  solvent  that  not  only  dissolves  electrolytes,  but 
breaks  them  down  into  ions  at  the  same  time.  Benzene  dissolves 
many  electrolytes,  but  does  not  dissociate  them,  and  therefore  such 
a  solution  would  be  a  non-conductor  of  the  electric  current. 

Chemical  affinity. — The  attraction  between  the  atoms  in  a  mole- 
cule, whether  due  to  electrical  attraction  or  other  forces. 

Specific  inductive  capacity. — Dielectric  constant.  We  owe  to 
Cavendish  (1771-81)  the  discovery  of  the  fact  that  the  amount: 
of  inductive  effect  which  takes  place  through  a  dielectric  is  different 
for  different  substances. 

Molecular  conductivity. — Molecular  conductivity  of  an  electrolyte 
is  equal  to  the  specific  conductivity  of  i  cubic  centimeter  of  the 
solution  times  the  number  of  cubic  centimeters  containing  a  gram- 
molecular  weight.  M  =  NS,  where  M  is  the  molecular  conductivity, 
N  the  number  of  cubic  centimeters  of  the  solvent  containing  the 
gram-molecular  weight  or  molugram  of  the  electrolyte,  and  S  the 
specific  conductivity  of  a  cubic  centimeter  of  the  solution. 


CHAPTER  IV. 

/ 

NOVEL   EXPERIMENTS    IN   "ELECTROLYTIC    INDUCTION." 

As  it  is  the  purpose  of  the  first  few  chapters  of  this  work  to  acquaint 
the  student  with  the  constitution  and  behavior  of  electrolytes  under 
various  conditions,  such  effort  would  fail  should  we  neglect  to  touch 
upon  the  electrostatic  and  electromagnetic  deportment  of  substances 
in  solution.  Having  dealt  with  electrolytes  theoretically  and  experi- 
mentally, and  learned  the  fundamental  laws  upon  which  their 
behavior  depends,  we  will  be  in  a  position  to  take  up  the  practical 
work  which  is  to  follow  in  the  later  chapters,  and  from  the  subject 
of  electrochemistry  as  a  science  touch  upon  electrochemical  engineer- 
ing as  an  art.  We  are,  therefore,  acquainting  ourselves  with  elec- 
trolytes, the  theories  upon  which  they  are  based,  and  their  capacities 
as  electrical  conductors.  We  shall  also  study  electrolytes  as  producers 
of  the  electric  current  but  this  phase  of  substances  in  solution  is 
best  left  until  a  little  later.  The  first  experiment  illustrating  the 
effects  of  electrical  induction  upon  an  electrolyte  as  given  in  Fig.  22 
was  designed  by  Wilhelm  Ostwald,  Professor  of  Chemistry  in  the 
University  of  Leipzig,  and  one  of  the  most  distinguished  physical 
chemists  Germany  has  ever  produced.  Prof.  Ostwald's  experiment 
has  for  its  object  to  prove  the  existence  of  "free  ions"  in  an  elec- 
trolyte, and  to  show  that  they  actually  migrate  and  carry  the  elec- 
trical charges  upon  them.  The  author  became  much  interested  in 
Ostwald's  work,  and  repeated  the  experiments  for  himself,  continuing 
the  research  still  farther,  as  will  be  described  in  the  present  chapter, 
developing  what  may  be  termed  "electrolytic  induction."  Let  us 
first  take  up  the  experiment  of  Ostwald  referring  to  the  illustration. 
In  the  experiment  with  potassium  chloride,  Ostwald  writes  as 
follows:  "The  following  consideration  may  serve  to  remove  the  last 
doubts  as  to  the  validity  of  the  assumption  of  free  electrically  charged 

50 


NOVEL  EXPERIMENTS   IN   "ELECTROLYTIC   INDUCTION."      57 

electrolyte  consisted  of  a  glass  tube  filled  with  a  dilute  solution  of 
sulphuric  acid.  It  was  necessary  to  introduce  in  series  with  the 
metal  coil  some  additional  resistance,  which  was  of  a  non-inductive 
type,  in  order  to  o'btain  comparable  conditions,  as  the  coil  of  elec- 
trolyte had  a  much  higher  ohmic  resistance  than  the  coil  of  wire. 
The  deflection  of  the  galvanometer  proved  to  be  the  same  in  both 
cases.  As  it  was  an  impossible  matter  to  place  the  magnet  in  the 
two  respective  solenoids  in  exactly  the  same  manner  and  at  exactly 
the  same  time,  the  experiment  as  illustrated  in  Fig.  26  was  conducted. 
Here  we  have  at  the  left  a  soft-iron  bar  running  horizontally  through 
a  coil  of  insulated  wire  which  is  in  series  with  a  storage-battery,  the 
terminals  of  the  wire  being  free  for  connection  with  a  contact  key 
which  may  be  closed  uniformly  any  number  of  times.  Next  to  the 
coil  we  have  a  glass  coil  filled  with  any  good  electrolyte  in  solution,, 
into  which  the  terminal  wires  (which  must  be  of  platinum)  of  a 
reflecting  galvanometer  dip.  At  the  extreme  right  we  have  a  coil  of 
resistance  wire  of  equal  proportions  and  equal  number  of  turns  as 
in  the  glass  coil,  and  in  series  with  it  a  rheostat  of  the  non-inductive 
type,  for  bringing  the  wire  to  the  same  resistance  as  the  coil  of  elec- 
trolyte. Of  course  some  wire  of  high  resistance  must  be  used,  such  as 
is  employed  in  resistance  sets,  in  order  that  we  will  not  have  to  depend 
upon  much  outside  resistance,  as  by  the  use  of  the  rheostat.  The 
coil  of  alloy  wire  may  now  be  substituted  for  the  coil  of  electrolyte, 
and  by  means  of  the  key  and  storage-battery,  operating  the  electro- 
magnet, we  can  produce  the  same  number  of  magnetic  lines  of  force 
in  just  the  same  way  and  in  the  same  time  as  we  did  in  the  case  of 
the  coil  of  electrolyte.  Experiments  with  such  a  piece  of  apparatus 
gave  the  same  deflections  of  the  galvanometer  with  a  coil  of  electrolyte 
as  they  did  with  a  coil  of  alloy  wire.  We  can  then  think  of  the  free 
ions  being  migrated  by  ordinary  magnetic  induction  so  common  to  all 
students  of  physics  and  electrical  engineering.  Let  us  now  study  the 
effect  of  an  electric  current  upon  a  magnetic  needle  while  traversing 
an  electrolyte.  For  this  purpose  set  up  a  piece  of  apparatus  like 
that  represented  in  Fig.  27.  Here  we  have  a  glass  tube  about  a  meter 
in  length  by  about  a  centimeter  in  internal  diameter,  bent  up  at  the 
ends  as  indicated.  This  is  filled  with  dilute  sulphuric  acid,  and  is 
provided  with  platinum  electrodes  with  loose-fitting  stoppers.  The 
tube  is  supported  on  two  laboratory  stands  above  a  delicate  compass- 


EXPERIMENTAL  ELECTROCHEMISTRY. 


needle  with  a  graduated  arc  or  scale.     There  are  also  two  upright 
standards  provided  with  insulators  between  which  an  alloy  wire  is 


11 


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- 


1! 


-a 

23 

0 


stretched  taut  at  the  same  height  as  the  glass  tube,  so  one  may  be 
substituted  for  the  other  above  the  magnetic  needle.     The  magnetic 


NOVEL  EXPERIMENTS  IN   "ELECTROLYTIC   INDUCTION."      59 


needle  is  represented  upon  an  adjustable  stand  in  order  that  it  may 
always  be  brought  to  exactly  the  same  distance  below  the  wire  and 
electrolyte  respectively.  The  measurement  must  be  made  from  the 
center  of  the  wire  and  electrolytic  tube  respectively.  Below  in  the 
same  illustration  we  have  a  plan  of  the  apparatus,  looking  down  upon 
it.  It  will  be  readily  seen  with  such  an  arrangement  how  the  wire 


PIG.  27. — Experiment  to  Show  the  Effect  of  Electrolytic  Conduction  upon  a  Magnetic 
Needle.  The  experiment  is  so  designed  that  a  wire  carrying  an  equal  current  of 
electricity  may  be  substituted  for  the  electrolyte  and  the  deflection  of  the  mag- 
netic needle  quantitatively  compared.  We  can  throw  in  series  with  the  electrolyte 
or  wire  at  will  the  lamp,  ammeter,  and  variablevrheostat  which  join  to  a  lighting 
circuit  or  storage-battery.  The  arrangement  of  the  two  switches  at  either  end 
will  make  this  clear. 

may  be  quickly  substituted  for  the  electrolyte,  and  how  the  electric 
current  may  be  controlled  and  made  to  flow  through  the  electrolyte. 
In  conducting  this  experiment  the  student  will  be  impressed  with 
the  greatly  superior  conductivity  of  metals  and  even  high-resistance 
alloys  over  electrolytes.  The  result  of  such  a  carefully  conducted 
experiment  will  show  that  the  magnetic  effect  of  electric  currents 
traversing  electrolytes  is  quantitatively  the  same  as  electric  currents 
of  equal  strength  traversing  conductors  of  the  first  class.  The  thought- 


60  EXPERIMENTAL   ELECTROCHEMISTRY. 

ful  student  will  be  likely  to  ask  why  the  effect  is  just  the  same  when 
we  have  positive  ions  going  to  the  cathode  carrying  positive  electrical 
charges  and  negative  ions  going  to  the  anode  carrying  negative  elec- 
trical charges.  The  only  answer  that  can  be  given  is  that  a  negative 
ion  traveling  from  right  to  left  tends  to  turn  the  magnetic  needle  in 
the  same  direction  as  a  positive  ion  does  traveling  from  left  to  right. 
We  know  that  the  same  current  traversing  a  wire  will  turn  a  magnetic 
needle  to  right  and  left  respectively,  according  to  its  position  above 
or  below  the  needle,  and  that  we  can  greatly  increase  the  magnetic 
effect  by  carrying  the  wire  over  and  under  the  needle  a  number  of 
times.  We  may  say  that  a  positively  charged  particle,  or  ion,  pro- 
duces the  same  effect  upon  a  magnetic  needle,  traveling  from  right 
to  left,  as  a  negatively  charged  ion  does  traveling  from  left  to  right. 
The  author  has  designed  an  elaborate  experiment  to  show  this  by 
a  rapidly  running  band  of  pure  silk  ribbon,  upon  which  are  pasted 
little  tinfoil  disks.  The  band  may  be  run  right-handedly  under  a 
suspended  magnetic  needle,  with  positive  static  charges  upon  the 
tinfoil  disks  and  the  deflection  and  direction  of  the  magnetic 
needle  noted.  The  direction  of  the  band  may  then  be  reversed,  and 
the  disks  be  charged  negatively,  when  the  deflection  and  direction 
of  the  needle  are  again  noted.  The  little  disks  are  charged  by  passing 
under  and  touching  a  tinsel  brush  connected  with  either  pole  of 
an  electrical  machine  of  the  static  type.  This  is  a  mechanical  repre- 
sentation of  migrating  ions  in  opposite  directions.  Owing  to  the 
small  quantity  charge  of  electricity  upon  the  disks  which  were 
placed  about  3  centimeters  apart  the  ribbon  was  run  at  high  speed. 
The  drums  over  which  the  ribbon  ran  were  supported  upon  solid 
glass  axles  to  insulate  the  same.  As  a  matter  of  fact  ions  travel  very 
slowly,  but  carry  very  large  charges  of  electricity.  In  the  running 
ribbon  we  have  very  small  charges  of  electricity,  and  therefore  to 
obtain  the  same  magnetic  effects  we  should  be  obliged  to  drive  the 
ribbon  and  little  tinfoil  disks  at  very  high  speed.  The  magnetic 
needle  must  therefore  be  protected  from  resulting  air-currents  in 
some  suitable  manner.  Having  seen  the  effects  of  electric  currents 
passing  through  electrolytes  on  magnetic  needles,  it  remains  only  to 
observe  the  effect  of  electric  currents  passing  through  electrolytes 
on  masses  of  ordinary  soft  iron.  Fig.  28  illustrates  a  simple  experi- 
ment to  measure  the  "magnetic  pull"  upon  a  soft-iron  bar,  if  such 


NOVEL  EXPERIMENTS   IN  "ELECTROLYTIC   INDUCTION."      6 1 

pull  exists.  At  the  right-hand  side  of  'he  diagram  we  have  an  analyt- 
ical ba  ance  with  the  left  pan  removed  in  order  that  we  may  suspend 
the  bar  of  soft  iron  to  be  experimented  upon.  Directly  under  the 
iron  bar  is  a  block  of  wood  or  other  suitable  support  for  the  glass  coil 
of  electrolyte.  The  platinum  electrodes  which  dip  into  this  electrolyte 
connect  through  an  open  scale,  or  delicate  ammeter,  in  series  with 
the  variable  rheostat  and  lamp-bank.  The  lamp-bank  described 
in  the  first  chapter  of  our  series  may  be  used.  We  can  now  by 
this  arrangement  admit  current  to  the  electrolytic  coil,  read  the 
current  in  amperes,  and  weigh  the  magnetic  pull  to  a  great  degree  of 
accuracy.  Substituting  the  alloy  coil,  we  can,  by  means  of  the  lamp- 
bank  and  variable  rheostat,  cause  the  same  current  to  flow  through 


FIG.  28. — Experiment  to  Show  and  Quantitatively  Measure  the  Magnetic  Pull  of  an 
Electrolyte  Carrying  an  Electric  Current.  At  the  left  is  an  ammeter,  a  variable 
rheostat,  and  a  lamp-bank;  above  the  ammeter  is  a  coil  of  alloy  wire  for  substi- 
tution purposes. 

the  alloy  coil  and  weigh  the  pull.  As  a  result  of  scores  of  tests  of 
this  character  the  author  found  the  pull  to  be  just  the  same  with  an 
electrolyte  as  it  was  with  a  wire  carrying  the  same  current.  Of 
course  it  goes  without  saying  that  the  convolutions,  and  consequently 
the  ampere-turns,  were  the  same  in  both  cases.  For  accurate  work 
it  must  be  impressed,  however,  that  a  rather  fine  wire  of  high  specific 
resistance  must  be  employed  for  the  conductor  of  the  first  class. 
Otherwise  the  resistance  of  the  wire  coil  will  be  so  much  less  than 
the  electrolyte  that  we  must  turn  in  a  great  deal  of  outside  resistance 
through  the  agency  of  the  rheostat.  Perhaps  the  most  interesting 
of  all  these  experiments  is  that  illustrated  in  Fig.  29,  which  has  been 
termed  a  demonstration  of  "  electrodeless  conduction."  Here  we 
have  simply  a  closed  system,  an  electrolyte  without  the  customary 


62 


EXPERIMENTAL  ELECTROCHEMISTRY. 


electrodes  for  giving  and  taking  the  electric  current.  Let  us  refer 
to  the  diagram  and  describe  the  method  of  showing  this  remarkable 
phenomenon.  The  illustration  represents  an  original  experiment  of 
the  author  performed  a  number  of  years  ago,  but  like  those  preceding, 
it  has  never  been  published.  A  represents  an  alternating-current 
generator  connected  to  a  coil  of  insulated  wire  on  the  spool  which 
encloses  a  soft-iron  bar.  This  soft-iron  bar  passes  into  a  glass  coil 
of  tubing  containing  dilute  sulphuric  acid,  and  is  joined  through 
two  straight  glass  tubes  about  a  meter  long  to  a  second  glass  coil 


FIG.  29. — Experimental  Demonstration  of  "  Electrodeless  Conduction."  A  repre- 
sents an  alternating-current  dynamo  connected  to  a  coil  of  insulated  wire;  through 
this  coil  a  soft-iron  bar  is  passed  which  enters  a  glass  coil  filled  with  an  electro- 
lyte;, this  glass  coil  is  connected  by  glass  tubes  with  a  second  glass  coil  which  is 
placed  within  a  calorimeter;  a  cylinder  of  thin  soft  Russia  iron  is  placed  within 
this  second  coil^  which  in  turn  received  a  very  sensitive  thermometer. 

filled  with  the  same  solution.  This  second  coil  of  electrolyte,  however, 
is  incased  within  a  calorimeter  made  from  a  common  pasteboard 
muff-box,  lined  within  with  hair  felt,  as  indicated  by  the  diagonal 
lines.  Within  this  coil  is  placed  a  small  cylinder  of  thin  Russia  iron, 
which  receives  in  turn  and  incloses  the  bulb  of  a  sensitive  thermometer, 
like  those  employed  in  our  previous  calorimeter  work.  One  of  Beck- 
mann's  thermometers  with  arbitrary  scale  and  reservoir  at  the  top  is 
an  excellent  type.  The  cover  is  placed  on  the  calorimeter,  and  after 
equilibrium  has  been  established  the  thermometer  is  read  and  the 


NOVEL  EXPERIMENTS   IN.  "  ELECTROLYTIC   INDUCTION."      65 

dynamo  started.  The  temperature  will  slowly  rise  when  within  the 
little  iron  cylinder.  If  the  cylinder  is  removed  the  mercury  in  the 
thermometer  will  fall  again,  and  rise  once  more  upon  lowering  the 
cylinder.  What  part  does  the  little  cylinder  play  ?  It  is  well  known 
to  all  physicists  and  most  electricians  that  iron  heats  up  when 
it  is  magnetized  first  in  one  direction  and  then  in  the  other 
by  the  alternating  current.  This  heating  of  iron  by  an  alternating 
current  under  such  circumstances  is  called  ''hysteresis."  Here  we 
have  the  heating  of  the  little  iron  cylinder  by  being  rapidly  magnetized 
first  in  one  direction  and  then  in  the  other,  which  gives  us  proof  that 
the  closed  system,  without  any  electrodes  whatever,  is  conducting 
the  electric  current.  On  breaking  the  system  anywhere,  with  the 
dynamo  still  in  operation,  the  heating  ceases.  Here  we  have  un- 
doubtedly the  ions  driven  first  in  one  direction  and  then  in  the 
other,  reversing  their  magnetic  effect  with  their  direction.  If  we 
could  insert  our  thermometer  in  the  electrolyte  itself,  we  would 
probably  get  a  heating  effect  due  to  the  "friction"  of  the  ions  among- 
themselves.  Fig.  30  illustrates  a  plan  for  carefully  studying  the 
effects  of  alternating  currents  upon  electrolytes  of  different  composi- 
tion. The  wiring  and  apparatus  is  so  arranged  in  this  experimental 
study  as  to  allow  of  supplying  alternating  currents  of  the  same 
energy  value,  but  of  various  frequencies.  It  has  been  shown  by  the 
writer  with  such  an  experimental  apparatus  that  the  frequency  of  the 
alternations,  everything  else  remaining  the  same,  has  a  decided 
effect  upon  electrolytes.  Only  a  very  few  years  ago  little  had  been 
done  with  the  alternating  current  as  applied  to  electrolytes,  and 
nothing  involving  alternating  currents  with  change  of  frequency. 
By  "frequency"  we  mean  the  number  of  double  reversals  of  the 
current  per  second.  The  frequency  varies  in  practice  between  25 
and  150.  The  term  "period"  used  in  connection  with  an  alternator 
denotes  the  time  elapsing  between  one  complete  reversal  of  the  cur- 
rent. Now  if  we  have  free  ions  in  solution  which  carry  the  electric 
current,  they  must  move  back  and  forth  to  some  extent  under  the 
influence  of  an  alternating  current.  In  other  words,  they  must 
oscillate.  Now  by  varying  the  frequency  of  our  alternations  we 
vary  the  rate  of  oscillation  of  the  ions,  and  if  the  heating  is  due  to- 
friction  between  the  ions,  the  heating  should  be  greater  at  higher 
frequencies  than  with  low  frequencies.  Such  was  found  to  be  the 


EXPERIMENTAL  ELECTROCHEMISTRY. 


NOVEL  EXPERIMENTS   IN   "ELECTROLYTIC   INDUCTION."       65 

case,  the  energy  value  of  the  alternating  current  being  kept  the  same. 
By  a  glance  at  the  last  illustration  we  can  readily  see  how  the  fre- 
quency may  be  changed  without  altering  the  energy  value  of  the 
current.  We  can  strongly  excite  the  fields  of  the  alternator  by  admit- 
ting a  heavy  current  through  the  rheostat  and  driving  the  alternator 
by  means  of  the  motor  at  low  speed,  when  we  will  obtain  an  alternating 
current  of  low  frequency  and  of  a  definite  energy  value.  We  can 
experiment  with  this  arrangement.  We  can  now  turn  in  our  rheostat 
and  admit  a  feeble  current  to  the  fields  of  the  alternator,  and  by 
driving  the  armature  at  a  high  speed  we  will  be  able  to  obtain  the 
same  energy  value  for  the  current,  but  at  high  frequency.  Experi- 
ments were  also  conducted  with  electrolytes  of  various  compositions, 
that  is,  with  light  and  heavy  ions  present  respectively.  The  electrolytes 
consisting  of  light  ions  invariably  heated  up  quicker  than  electrolytes 
with  heavy  ions.  This  can  only  be  explained  on  the  ground  of  inertia. 
The  lighter  ions  travel  through  the  greater  distances  when  oscillating, 
and  therefore  collide  a  greater  number  of  times.  The  heavier  ions, 
because  of  their  greater  inertia,  do  not  respond  so  readily  to  the 
alternations,  and  therefore  move  through  a  lesser  distance.  They 
consequently  do  not  meet  with  so  many  collisions,  and  the  friction 
is  reduced.  This  of  course  is  theory,  but  the  fact  of  experimental 
investigation  remains  that  the  lighter  ions  cause  a  more  rapid  heating 
than  heavy  ions,  and  that  all  electrolytes  heat  up  more  quickly  with 
alternating  currents  of  high  frequency  than  they  do  with  alternating 
currents  of  low  frequency.  It  only  remains  for  us  to  find  a  theory 
to  account  for  the  facts. 


CHAPTER  V. 
THE  VELOCITY  OF  ELECTROLYTIC  CONDUCTION. 

EXPERIMENTS  WITH  A  HIGH-SPEED  SPECIAL  CHRONOGRAPH  CAPABLE 
OF   DIVIDING   A   SECOND   INTO   A   MILLION   PARTS. 

Absolute  Velocity  of  Ions. 

IT  will  be  recalled  that  in  the  preceding  chapter  ions  were  made 
to  travel  by  induction.  In  the  experiment  with  the  electrical  ma- 
chine the  two  vessels  connected  by  means  of  the  wet  string,  and 
the  capillary,  the  electrostatic  charging  of  the  electrolyte  took  place 
at  once.  In  other  words,  as  soon  as  the  electrical  machine  was 
started,  bubbles  of  hydrogen  gas  made  their  sudden  and  immediate 
appearance  within  the  capillary.  Now,  as  a  matter  of  fact,  the 
bubbles  of  gas  would  make  their  appearance  at  once,  whether  this 
wet-string  conductor  was  long  or  short.  The  electrical  conduction 
would  be  instantaneous,  and  yet  we  will  learn  a  little  later  in  the 
present  chapter,  under  the  heading  "Absolute  Velocities  of  the  Ions," 
that  the  ions  themselves  move  very  slowly  and  have  different  veloci- 
ties. How  can  we  account,  therefore,  for  the  instantaneous  con- 
duction of  an  electrolyte,  when  the  ions  which  carry  the  electricity 
upon  them  move  very  slowly  and  have  their  respective  velocities? 
We  can  only  account  for  the  facts  in  such  an  experiment  by  attrib- 
uting the  instantaneous  conduction  to  be  due  to  free  ions  already 
present  about  the  electrodes.  Fig.  31  represents  an  experiment 
of  Prof.  Ostwald  to  show  the  instantaneous  electrical  conduction 
through  electrolytes.  Here  we  have  a  glass  tube  about  50  centi- 
meters long  and  i  centimeter  in  diameter  bent  at  right  angles  at 
the  ends  and  enlarged  into  cylindrical  terminals  as  shown.  At 
the  left  we  have  a  stick  of  chemically  pure  zinc  supported  in  posi- 
tion by  a  cork.  At  the  right  we  have  a  bent-tube  manometer  con- 

66 


THE   VELOCITY   OF  ELECTROLYTIC   CONDUCTION. 


67 


taining  a  little  colored  water,  supported  by  a  good  tight  cork  also. 
At  the  bend  on  the  right  a  platinum  wire  is  fused  in  place  to  act 
as  the  other  terminal  or  electrode.  The  tube  is  filled  with  dilute 
sulphuric  acid.  Upon  connecting  this  piece  of  apparatus  with  a 
battery,  motor-generator,  or  lamp-bank  as  described  in  the  first 
chapter,  making  the  zinc  the  anode  and  the  platinum  wire  the  cathode, 
bubbles  of  hydrogen  appear  instantly  upon  the  platinum  wire,  and 
a  pressure  is  indicated  upon  the  water-gauge.  The  instantaneous 
appearance  of  bubbles  of  hydrogen  with  the  closing  of  the  contact 


FIG.  31. — Prof.  Ostwald's  Experiment  to  show  Instantaneous  Electrical  Conduction 
through  an  Electrolyte. 

key  in  series  with  the  source  of  electricity  goes  to  prove  the  presence 
of  free  ions  already  about  the  electrodes.  These  free  ions  merely 
give  up  their  charges  and  escape  upon  completing  the  circuit.  Now,, 
if  it  was  necessary  for  the  electric  current  to  first  decompose  or  break 
up  the  molecule  of  sulphuric  acid,  then  the  two  atoms  of  hydrogen 
replaced  by  the  zinc  in  the  SO 4  radical,  must  have  traveled  to  the 
platinum-wire  cathode  through  the  tube,  which  is  50  centimeters 
long.  Now  there  are  experiments,  as  we  shall  see  at  the  close  of 
this  chapter,  to  determine  the  absolute  velocities  of  ions,  and 
measurements  upon  the  velocity  of  the  hydrogen  ion  show  that  it 
would  require  a  long  time  for  hydrogen  ions  to  travel  through  a 


68  EXPERIMENTAL   ELECTROCHEMISTRY. 

tube  50  centimeters  long.  Now,  hydrogen  appears  at  once  upon 
closing  the  circuit,  and  we  must  attribute  the  immediate  response 
or  conductivity  of  the  solution,  to  free  ions  already  around  the  elec- 
trodes in  readiness  to  discharge  their  electricity.  Although  this 
experiment  of  Prof.  Ostwald  is  one  of  great  interest,  it  struck  the 
present  writer  as  being  very  crude  and  rough  and  capable  of  great 
improvement.  It  does  not  answer  many  vital  questions.  For 
•example,  do  all  electrolytes  conduct  with  the  same  velocity?  In 
other  words,  will  an  electrolyte  consisting  of  heavy  ions  respond 
or  conduct  as  quickly  as  an  electrolyte  consisting  of  light  ions? 
Will  all  electrolytes  conduct  as  quickly  as  a  metallic  conductor? 
This  appeared  to  be  neglected  as  a  piece  of  research  work;  and 
with  a  view  of  comparing  different  electrolytes  with  each  other 
both  in  solution  and  in  igneous  fusion,  and  in  comparing  electrolytes 
with  metallic  conductors,  the  special  high-speed  chronograph  was 
designed  and  built  as  illustrated  in  the  following  drawings.  Through 
the  agency  of  this  chronograph,  a  dynamo  current  was  compared 
with  the  current  from  a  set  of  accumulators,  and  light  thrown  upon 
such  questions  as  mechanical  movement  of  ions  of  different  weights, 
involving  the  question  of  inertia.  Let  us  first  compare  electrolytic 
conduction  in  an  electrolyte  with  metallic  conduction,  for  if  the  two 
act  in  the  same  time,  the  evidence  in  favor  of  free  ions  is  strength- 
ened. Fig.  32  outlines  in  diagram  the  chronograph  cylinder  and 
the  electrolyte  and  wire  respectively.  Here  A  represents  the  elec- 
trolyte in  the  glass  tube,  and  B  the  parallel  metallic  conductor. 
C  is  a  rheostat  in  series  with  the  metallic  conductor  to  bring  the 
same  to  an  equal  ohmic  resistance  with  the  electrolyte.  D  repre- 
sents a  delicate  ammeter  in  series  with  the  electrolyte  and  the  electro- 
magnet E  of  the  chronograph.  F  represents  in  dotted  lines  the 
same  ammeter  shifted  in  series  with  the  metallic  conductor  and  the 
electromagnet  G  of  the  same  chronograph.  H  illustrates  a  double 
switch  for  simultaneously  closing  both  circuits  after  the  resistances 
of  the  two  have  been  balanced  or  made  carefully  equal  to  each 
other.  By  revolving  the  chronograph  cylinder  and  closing  the 
switch,  the  two  electromagnets  will  strike  the  paper  band  upon 
the  chronograph  cylinder  and  draw  records  by  means  of  soft  lead- 
pencil  points.  The  chronograph  and  magnets  must  first  be  most 
carefully  calibrated  on  one  and  the  same  circuit  by  connecting  the 


THE  VELOCITY  OF  ELECTROLYTIC  CONDUCTION. 


69 


magnets  in  series  with  each  other,  thereby  supplying  a  common, 
current  of  electricity,  and  adjusting  their  springs  and  striking  dis- 
tances until  a  current  of  common  value  will  cause  both  magnets  to 
strike  upon  the  rapidly  revolving  cylinder  at  the  same  instant.  This. 


FIG.  32. — Diagram  of  Author's  Method  of  Studying  Time  Required  for  Electric  Cur- 
rents to  Traverse  Electrolytes,  and  to  Compare  the  Time  with  that  Required  by 
Metallic  Conductors.  A,  electrolyte;  B,  parallel  wire;  C,  rheostat  for  balancing 
resistance  of  wire  to  that  of  electrolyte;  D,  mill-ammeter  in  series  with  electro- 
lyte and  magnet  E;  at  F  the  mill-ammeter  is  shown  shifted  in  series  with  wire 
and  magnet  G;  H,  double  switch  for  closing  both  circuits  simultaneously. 

can  most  easily  be  seen  by  the  pencil  records.  When  by  careful 
experiment  and  adjustment  the  two  electromagnets  strike  "abreast"" 
upon  the  flying  cylinder,  which  is  driven  by  a  high-speed  elecrtic 
motor,  the  series  connection  is  changed  and  each  electromagnet; 
is  placed  separately  in  circuit  with  electrolyte  and  wire  respectively, 
previously  made  of  equal  ohmic  resistance.  The  lines  upon  the 


70  EXPERIMENTAL   ELECTROCHEMISTRY. 

cylinder  in  this  drawing  illustrate  the  appearance  of  the  pencil 
record  when  the  cylinder  is  driven  at  moderately  high  speeds.  A 
photograph  of  such  a  chronograph  is  given  in  Fig.  33,  where  an 
electric  motor  is  directly  connected  by  means  of  a  flexible  coupling 
to  reduce  vibration.  It  was  soon  found,  however,  with  such  a 


FIG.  33. — Photograph  of  Simple  Drum  High-speed  Chronograph  Direct  Connected  to 

Electric  Motor. 

simple  chronograph  cylinder,  when  driven  at  very  high  speeds, 
that  the  pencil  records  were  drawn  all  the  way  around,  and  it  was 
impossible  to  see  where  the  contacts  were  first  made.  It  became 


FIG.  34. — Rear  View  of  Electrochronograph  provided  with  Electric  Motor,  Balance- 
wheel,  and  Revolution-counter.  This  instrument  is  a  modification  of  that  shown 
in  Fig.  3,  as  it  drives  a  long  band  of  paper  for  receiving  record. 

necessary  to  expand  the  chronograph  by  driving  a  long  band  of 
paper.     Figs.  34  and  35  will  make  the  plan  clear.     In  Fig.  34  the 


THE  VELOCITY   OF  ELECTROLYTIC   CONDUCTION. 


end  of  the  chronograph  cylinder  is  again  shown,  with  its  electric 
driving  motor  at  the  right,  and  with  a  heavy  balance-wheel  to  steady 


its 
at 


rapid  motion  at  the  left,    A  revolution  counter  is  also  depicted 
the  extreme  left,  pressed  against  the  shaft  of  the  chronograph 


72  EXPERIMENTAL   ELECTROCHEMISTRY. 

cylinder.  This  revolution  counter  was  afterward  moved  to  the 
shaft  of  the  pulley  at  the  far  end  of  the  band,  as  being  a  fairer  place, 
for  in  case  there  was  a  slight  creeping  of  the  band  upon  the  chrono- 
graph cylinder,  there  would  be  no  error  introduced  from  this  cause. 
Fig.  35  illustrates  a  side  view  of  this  special  form  of  band  chrono- 
graph, showing  its  band  and  supporting  drum-wheel  at  the  far  end 
of  the  work-table  over  which  it  runs.  The  arrangement  of  the 
marking-pencils  and  electromagnets  is  made  clear  in  this  illus- 
tration. Upon  the  work  bench  or  table  are  the  electrolyte  and 
wire  respectively,  together  with  a  cell  or  storage  battery  and  a 
special  form  of  U  tube  used  for  various  conduction  experiments 
with  electrolytes.  This  particular  chronograph  revolves  at  the 
rate  of  two  thousand  revolutions  per  minute,  and  it  will  be  seen 
that  the  slightest  "lag"  in  conductivity  in  either  circuit,  when  the 
two  are  closed  simultaneously  by  a  proper  key,  will  be  shown  accu- 
rately and  quantitatively  upon  the  moving  band.  With  this  ar- 
rangement, as  will  be  seen  from  the  following  mathematical  exposi- 
tion, a  second  may  be  divided  into  one  hundred  thousand  parts; 
and  by  higher  speeds,  the  second  may  be  laid  off  and  divided  into  a 
million  parts,  dependent  upon  the  behaviors  of  the  various  con- 
ductors experimented  with.  The  diameter  of  the  chronograph 
cylinder  being  15  centimeters,  we  can  take  this  as  a  basis  upon 
which  to  start  the  calculation. 


15  cm.  diameter 


1570795 


47-12385  cm.  circumference 

With  2000  revolutions  per  minute,  we  have  47.12385X2000  = 
94247.70  centimeters  per  minute.  The  space  traveled  during  one 
second  is  therefore 

60)94247.70(1504.1283  cm. 

In  i/  10  second        we  have  150.41283  cm. 
In  i/  100  second  "  15.041283  cm. 

In  i/iooo  second         "  1.5041283  cm. 

In  i/ioooo  second       "  .15041283  cm. 


THE   VELOCITY  OF  ELECTROLYTIC   CONDUCTION.  73 

Working  with  a  chronograph  of  still  higher  speed,  the  cylinder 
being  driven  by  a  two-horse-power  motor  belted  up  for  speed,  the 
scale  upon  the  flying  band  was  of  course  still  more  open,  and  allows 
of  determinations  to  be  made  to  1/100,000  and  even  1/1,000,000  of 
a  second.  A  tabulated  length  of  spaces  upon  this  high-speed  band 
is  as  follows  up  to  hundred- thousandths  of  a  second.  The  figures  are 
as  follows: 

Cm.  Circumference.  Rev.  per  Min.  Cm.  Traveled.  • 

47.12385         X         10000     =     471238.5  cm.  per  min. 

60)471238.5(7853.97500  cm.  per  second. 
In  i/io  second  we  have  785.397500  cm. 

In  i/ioo  second  "  78.5397500  cm. 

In  i/iooo  second  "  7-853975°° cm- 

In  i/ioooo  second  "  -7853975°° cm- 

In  i/ioooooo  second         "  .0785397500  cm. 

For  higher  speeds  still  and  correspondingly  more  minute  subdivisions 
of  the  second,  a  chronograph  rigged  like  that  shown  in  Fig.  36  was 
experimented  with.  Here  we  have  an  electrolyte  50  feet  long  in  the 
glass  tube  arranged  like  a  steam-radiator,  and  the  chronograph 
cylinder  driven  at  enormous  speed  by  the  multiplying  system  of 
belting  to  the  countershaft,  etc.  The  telephone-receiver,  cell  of 
battery,  induction-coil,  and  resistance  set  depicted  here  were  employed 
to  balance  the  resistances,  instead  of  the  ammeter  employed  in 
the  slower-speed  design  of  instrument.  The  method  of  measuring 
resistances  by  means  of  the  telephone  and  induction-coil  is  known  as 
Kohlrausch's  method,  and  consists  of  the  simple  Wheatstone  bridge 
arrangement,  with  a  telephone-receiver  in  the  place  of  a  galvanometer, 
and  the  alternating  current  from  the  secondary  of  a  small  induction- 
coil  instead  of  a  simple  battery  of  cells.  With  this  arrangement  the 
alternating  current  produces  a  humming  sound  in  the  telephone 
when  the  bridge  is  out  of  balance.  The  alternating  current  in  addi- 
tion does  not  decompose  the  electrolyte,  and  allows  of  conductivity 
determinations  being  made  with  great  accuracy.  Having  described 
the  apparatus,  some  of  the  results  will  now  be  given.  The  first 
experiments  were  made  with  an  electrolyte  consisting  of  dilute  sul- 
phuric acid  in  the  proportion  of  10  cubic  centimeters  of  H2SO4, 
specific  gravity  1.84664,  in  40  cubic  centimeters  of  distilled  water,  and 


74 


EXPERIMENTAL   ELECTROCHEMISTRY. 


a  wire  of  German  silver  made  equal  in  resistance  by  means  of  a 
rheostat  of  the  non-inductive  type.    This  is  an  important  point  to 


observe  in  determining  all   resistances  where  only  a  momentary 
current  is  to  be  dealt  with.     For  a  dissertation  upon  the  subject  of 


THE  VELOCITY  OF  ELECTROLYTIC   CONDUCTION.  75 

non-inductive  resistances,  the  student  must  be  referred  to  any  standard 
work  on  physics  dealing  with  electrical  measurements.  The  present 
writer  may  say,  however,  that  with  common  coil  resistances,  or 
rheostats,  there  is  a  choking  or  damping  effect  upon  electrical  impulses 
of  short  duration,  due  to  the  phenomenon  of  self-induction.  Having 
balanced  the  respective  resistances  of  the  electrolyte  and  wire  with 
its  non-inductive  resistance  rheostat  in  series,  the  chronograph  was 
speeded  up,  and  when  a  rate  of  2000  revolutions  per  minute  was 
reached,  as  counted  by  the  revolution-counter  upon  the  drum-wheel 
shaft,  the  key  was  closed  three  times  in  rapid  succession  and  the 
chronograph  stopped.  Three  records  had  been  made.  At  first  it 
was  found  that  the  electromagnet  in  series  with  the  electrolyte 
struck  a  trifle  in  advance  of  the  electromagnet  in  series  with  the 
wire,  the  marking  on  the  band  leading  by  0.75  centimeter,  indicating 
that  the  conductivity  through  the  electrolyte  was  ahead  by  i/ 10,000 
of  a  second.  What  was  this  due  to  ?  Although  the  two  resistances 
were  balanced  as  carefully  as  possible,  the  leading  of  the  electrolyte 
was  undoubtedly  due  to  the  fact  that  its  resistance  was  slightly 
lower  than  that  of  the  wire.  The  resistances  were  carefully 
rebalanced,  using  the  most  refined  means,  when  the  two  con- 
ductors finally  "struck  abreast,"  so  to  speak,  upon  the  flying 
band.  Electrolytes  of  various  composition  were  substituted  for 
the  sulphuric  acid  and  carefully  compared  with  the  wire,  and 
in  every  case  where  the  resistances  had  been  perfectly  balanced 
the  two  electromagnets  struck  abreast.  The  highest  speeds  of 
bands  were  of  course  obtained  with  the  large  instrument  as  shown 
in  Fig.  36,  and  with  this  equipment,  electrolytes  of  various  lengths 
were  experimented  with.  An  electrolyte  50  feet  in  length  conducted 
as  quickly  as  an  electrolyte  only  a  few  centimeters  long.  It  mattered 
not  whether  we  used  an  electrolyte  with  light  or  heavy  ions,  the  rate 
of  conductivity,  or  response  to  the  electric  current,  was  the  same. 
Experiments  were  also  conducted  with  storage-batteries  as  a  source 
of  electricity,  and  it  was  recorded  here  again  that  the  electricity  left 
the  free  ions  in  the  storage-cells  as  readily  as  it  did  a  wire  charged 
by  a  dynamo  current.  Experiments  of  this  character  were  repeated 
many  times,  and  the  writer  believes  one  is  justified  in  stating  the 
law  that  electrolytes  of  equal  resistance  conduct  the  electric  current  with 
a  definite  velocity  regardless  of  the  composition  of  the  electrolytes  or  the 


7 6  EXPERIMENTAL   ELECTROCHEMISTRY. 

length  oj  the  containing  vessel.  It  may  also  be  stated  that  an  elec- 
trolyte conducts  the  electric  current  as  quickly  as  a  conductor  of  the  first 
class,  regardless  of  its  composition,  provided  we  have  an  equal  ohmic 
resistance  oj  a  non-inductive  type.  In  working  with  fused  electrolytes 
the  same  quantitative  behavior  was  observed,  the  electric  current 
flowing  as  quickly  after  contact  as  with  all  metallic  conductors. 
Free  ions  must  therefore  be  around  the  electrodes  and  in  contact 
with  them.  If  molecules  had  to  be  first  broken  down  into  ions,  and 
these  ions  had  to  travel,  there  would  undoubtedly  be  a  lag  in  experi- 
menting with  electrolytes  consisting  of  heavy  ions,  for  the  question 
of  inertia  would  be  involved.  The  same  impulse  which  would  start 
up  light  ions  in  a  given  time  would  fail  to  produce  the  same  response 
where  heavier  ions  were  concerned.  Having  shown  the  instantaneous 
behavior  of  electrolytes  toward  the  electric  current,  we  are  now  in  a 
position  to  study  the  experimental  methods  for  measuring  the  abso- 
lute velocity  of  ions. 

Experimental  Methods  for  Showing  the  Absolute  Velocity  of  Ions. 

Lodge's  Apparatus. 

It  has  been  stated  that  all  ions  had  their  respective  velocities,  and 
that  these  velocities  were  exceedingly  small.  It  has  been  demon- 
strated by  Bredig,  and  also  by  Ostwald,  that  the  velocity  or  mechanical 
motion  of  the  ions  is  a  function  of  their  atomic  weights.  This  rela- 
tionship was  brought  out  by  series  of  long  and  patient  research, 
but  the  reason  for  such  behavior  is  not  understood.  We  have  in 
chemistry  several  striking  cases  of  periodic  behavior,  although  we 
have  so  far  been  unable  to  account  for  them.  If  we  arranged  the 
ions  in  a  table  according  to  their  migration  rates,  we  would  find  that 
hydrogen  is  the  swiftest  of  them  all,  although  its  movement  through 
an  electrolyte  requires  considerable  time.  Let  us  look  into  the 
method  of  Lodge,  and  learn  just  what  the  speed  of  the  hydrogen  ion 
is.  Fig.  37  illustrates  the  apparatus  of  this  physicist  for  determining 
the  speed  of  the  hydrogen  ion  under  a  given  potential  gradient. 
Here  we  have  two  beakers  or  glass  jars  joined  by  a  siphon-tube  bent 
at  right  angles  at  each  end.  A  centimeter-scale  is  attached  to  the 
under  side  of  this  tube  as  indicated.  This  glass  siphon-tube  contains 
an  aqueous  solution  of  gelatine  put  in  hot,  which  solidifies  when 


THE   VELOCITY   OF   ELECTROLYTIC    CONDUCTION. 


77 


cold,  forming  a  jelly.  Now  this  solution  of  gelatine  also  contains 
some  sodium  chloride,  NaCl,  to  serve  as  the  electrolyte,  and  the 
entire  solution  is  colored  red  by  the  addition  of  a  little  phenolphtha- 
lein made  alkaline  with  a  few  drops  of  sodium-hydroxide  solution. 
The  gelatine  is  dissolved  in  hot  water  in  a  beaker  and  some 
common  salt  is  added  and  stirred  until  a  perfectly  homogeneous 
solution  is  obtained.  A  little  phenolphthalein  is  then  stirred  in 
and  made  red  by  adding  a  few  drops  of  the  sodium-hydroxide 
solution.  This  mixture  is  kept  near  the  boiling-point  of  water  for 
a  few  minutes,  and  is  then  poured  into  a  number  of  tubes  bent  at 


1 


r 


FIG.  37. — Lodge's  Apparatus  for  Experimentally  Determining  the  Absolute  Velocity 

of  the  Hydrogen  Ion. 

right  angles  to  form  siphons  like  that  illustrated.  Care  must  be 
taken  to  avoid  the  inclosing  of  air-bubbles,  and  the  tubes  are  put 
away  to  cool  and  solidify  with  the  bent  ends  turned  up.  To  measure 
the  velocity  of  the  hydrogen  ion,  one  of  the  tubes  after  cooling  is  placed 
dipping  into  the  two  beakers  as  shown,  and  the  beakers  filled  with  a 
dilute  solution  of  sulphuric  acid.  Two  platinum  electrodes  are  put  in 
place  and  connected  to  our  motor-generator  or  lamp-bank,  with  a 
voltmeter  joined  across  the  electrodes  to  show  the  potential  gradient 
under  which  we  are  working.  All  ions  have  a  fixed  velocity  under  a 
;set  potential  gradient.  Now,  what  takes  place  when  a  current  of 
electricity  is  made  to  pass  through  this  system?  The  hydrogen  ion 
from  the  electrolyte  of  sulphuric  acid  starts  from  the  anode  in  the 
right-hand  beaker  and  makes  its  way  to  the  cathode  in  the  left- 
hand  beaker  through  the  composition  in  the  siphon-tube.  What 
happens  there?  The  hydrogen  simply  displaces  the  sodium  from 
the  sodium  chloride  present  and  forms  hydrochloric  acid,  H  +  NaCl  = 
HC1,  which  decolorizes  the  gelatinous  solution  of  phenolphthalein. 


78  EXPERIMENTAL   ELECTROCHEMISTRY. 

This  indicator  is  red  in  the  presence  of  a  base  and  colorless  in  the 
presence  of  an  acid.  As  the  hydrogen  ion  proceeds  through  the 
siphon-tube,  it  replaces  the  sodium  in  the  sodium  chloride,  and 
bleaches  out  the  phenolphthalein  marking  its  way  through  the 
composition.  The  experiment  is  an  interesting  one  to  watch,  as  the 
decoloration  proceeds  at  a  slow  rate.  Lodge  worked  with  a  potential 
gradient  equivalent  to  a  drop  of  one  volt  a  centimeter.  If  we  have 
a  tube  50  centimeters  long,  therefore  we  must  use  a  difference  in 
potential  of  50  volts,  and  must  employ  our  lamp-bank  for  this,  unless 
we  have  at  hand  a  dynamo  wound  for  a  current  output  at  50  volts. 
For  a  short  tube  we  can  use  our  motor-generator.  Working  with 
such  a  piece  of  apparatus  with  a  drop  of  one  volt  per  centimeter, 
Lodge  found  the  absolute  velocity  of  the  hydrogen  ion  to  be  about 
if  centimeters  per  minute.  In  three  determinations  Lodge  found  the 
hydrogen  ion  to  travel : 

1.1560  centimeters  per  minute. 
1.1740  "  "        " 

1.1440 

The  average  of  these  three  determinations  with  the  above  apparatus 
being  1.1580  centimeters  per  minute,  or  considerably  over  an  hour 
for  this,  the  swiftest  of  all  ions,  to  travel  a  meter;  and  yet  as  shown 
by  the  electrochronograph  work,  an  electric  current  leaps  through 
an  electrolyte,  so  to  speak,  in  exactly  the  same  time  as  it  does 
through  a  wire. 

Whetham's  Method. 

Another  experimental  method  for  determining  the  absolute 
velocities  of  ions  was  devised  and  used  by  Whetham,  the  apparatus 
being  illustrated  in  Fig.  38.  He  describes  his  method  as  follows: 
"Suppose  we  have  two  solutions  like  copper  chloride  and  ammonium 
chloride,  containing  one  ion  in  common  and  having  nearly  equal 
conductivities.  Let  one  solution  be  colored  and  have  a  density 
different  from  that  of  the  other.  The  denser  solution  is  first  poured 
into  the  longer  arm  of  a  kind  of  U  tube,  and  then  the  other  is  allowed 
to  flow  gently  on  to  its  surface  from  the  shorter  arm.  If  a  current 
is  passed  across  the  junction  between  the  two  solutions,  it  carries 
the  copper  and  ammonium  ions  with  it  and  drives  the  chlorine  ions  in 


THE   VELOCITY   OF  ELECTROLYTIC   CONDUCTION. 


79 


the  opposite  direction.  Since  the  color  depends  on  the  presence  of 
the  copper  ions,  the  boundary  will  travel  with  the  current,  and  by 
measuring  its  velocity  the  speed  of  the 
ions  under  unit  potential  gradient  can 
be  calculated."  There  are  several  other 
methods  for  determining  absolute  veloci- 
ties of  ions,  and  in  the  hands  of  careful 
investigators  the  results  agree  very  strik 
ingly.  As  will  be  seen  later,  there  are 
methods  for  determining  the  relative 
velocities  of  the  ions,  and  it  will  be  seen 
at  once  if  we  have  the  absolute  velocity 
of  one  ion  accurately  determined,  and 
we  can  ascertain  in  other  ways  the  rela- 
tive velocities  of  the  remaining  ions,  we 
can  calculate  the  absolute  velocities  of 
them  all.  Having  learned  about  electro- 
lytes, dissociation,  ionic  velocity,  etc.,  we 
will  be  in  a  good  position  to  take  up 
and  appreciate  work  of  a  little  more 
practical  character  in  our  next  chapter, 
and  introduce  the  student  to  the  beauti- 
ful work  of  Faraday  in  electrochemical 
science.  Here  we  will  study  the  quantitative  relation  of  the  electric 
current  to  electrolytes,  and  take  up  the  energy  relations  between 
chemistry  and  electricity,  and  lay  the  foundation  for  work  of  a  very 
practical  and  useful  character. 


FIG.  38. — Whetham's  Appara- 
tus for  Experimentally  Deter- 
mining the  Absolute  Veloci- 
ties of  Ions. 


CHAPTER  VI. 
FARADAY'S    LAW. 

DISTINCTION  BETWEEN  CURRENT  REQUIRED  AND  ENERGY  ABSORBED. 
EXPERIMENTS   TO   SHOW  MECHANICAL   MOVEMENT   OF   MATERIAL. 

THE  idea  occurred  to  Faraday  to  send  a  current  through  several 
electrolytes  connected  up  in  series,  and  to  make  weighed  compari- 
sons of  the  materials  separated  by  the  same  current  in  a  given  time. 
In  1883,  the  result  of  Faraday's  most  important  and  valuable  work 
was  framed  into  the  following  law  by  H.  Von  Helmholtz: 

"The  same  quantity  of  electricity  passing  through  an  electrolyte 
either  sets  jree  or  transfers  to  other  combinations  always  the  same 
number  of  valencies." 

Von  Helmholtz,  in  his  "Faraday  lecture"  delivered  in  London, 
on  April  5,  1881,  laid  the  foundation  of  a  new  electrochemical  theory 
which  explains. the  facts  embraced  by  Faraday's  law.  The  most 
important  of  these  facts  may  be  stated  in  this  sentence: 

"Every  single  valency  of  an  elementary  or  compound  ion  is 
charged  with  exactly  the  same  quantity  of  positive  or  negative 
electricity,  which  behaves  as  if  it  were  an  electrical  atom  that  can- 
not be  further  divided." 

As  the  work  of  Faraday  is  of  such  great  moment  in  theoretical 
and  practical  electrochemistry,  the  actual  words  of  Von  Helm- 
holtz are  given,  the  author  believing  that  the  facts  as  learned  by 
Faraday  are  among  the  first,  if  not  the  most  important,  of  all  here 
recorded.  The  words  used  by  Von  Helmholtz  are  these,  as  trans- 
lated by  M.  M.  Patterson  Muir: 

"  The  same  definite  quantity  of  either  positive  or  negative  elec- 
tricity moves  always  with  each  univalent  ion,  or  with  every  unit 
of  affinity  of  a  multivalent  ion,  and  accompanies  it  during  all  its 

motions  through  the  interior  of  the  electrolytic  fluid. 

80 


FARADAY'S   LAW. 

"  This  quantity  we  may  call  the  electric  charge  0}  the  atom. 

11  If  we  accept  the  hypothesis  that  the  elementary  substances  are 
composed  of  atoms,  we  cannot  avoid  concluding  that  electricity  also, 
positive  as  well  as  negative,  is  divided  into  definite  elementary  por- 
tions, which  behave  like  atoms  of  electricity.  As  long  at  it  moves 
about  in  the  electrolytic  fluid,  each  ion  remains  united  with  its 
electric  equivalent  or  equivalents.  -  - 

11  At  the  surface  oj  the  electrodes  decomposition  can  take  place 
if  there  is  a  sufficient  electromotive  jorce,  and  then  the  ions  give 
of)  their  electric  charges  and  become  electrically  neutral.''1 

From  this  work  the  valuable  table  of  electrochemical  equivalents 
was  compiled,  which  is  of  the  utmost  importance  in  all  practical 
electrochemical  work.  The  definition  of  an  electrochemical  equiva- 
lent being  capable  of  expression  in  several  ways,  it  should  be  care- 
fully studied  and  appreciated.  If  the  quantities  of  all  ions  which 
stand  to  one  another  in  the  relations  of  their  combining  weights 
carry  equal  quantities  of  electricity,  it  will  at  once  be  appreciated 
that  it  is  of  great  scientific  importance  to  know  the  exact  amount 
of  electricity  which  a  unit  quantity  of  ions  will  carry.  This  can  be 
determined  by  passing  a  given  quantity  of  electricity  through  a 
solution  of  an  electrolyte  and  weighing  the  amount  of  metal  de- 
posited upon  the  cathode,  or  measuring  the  amount  of  gas  liberated 
and  calculating  its  weight  from  its  volume.  This  has  been  done 
very  carefully  by  Lord  Rayleigh  and  Mrs.  Sedgewick,  who  found 
that  one  coulomb  of  electricity  deposits  1.1179  milligrams  of 
silver.  W.  and  F.  Kohlrausch,  working  with  equal  care,  found 
under  the  same  conditions  1.1183  milligrams.  The  mean  of 
these  figures  is  1.1181  milligrams.  A  more  recent  determina- 
tion of  the  electrochemical  equivalent  of  silver  by  Richards,  Col- 
lins, and  Heimrod  gives  1.1172  milligrams  of  silver  as  equiva- 
lent to  one  coulomb.  A  still  more  recent  determination  by  Pat- 
terson and  Guthe  gives  the  slightly  larger  value  of  1.1192  milli- 
grams as  equivalent  to  one  coulomb.  This  agrees  with  the  mean 
result  obtained  by  Pellat  and  Portier,  and  is  very  close  to  the 
number  obtained  by  Kahle,  1.1193.  The  mass  of  the  ions  taken  is 
purely  arbitrary.  Here,  as  in  so  many  other  cases,  it  is  convenient 
to  use  the  gram-molecular  weight  for  univalent  and  the  gram- 
equivalent  weight  for  polyvalent  ions.  For  all  practical  purposes 


82  EXPERIMENTAL  ELECTROCHEMISTRY. 

the  electrochemical  equivalent  of  silver,  which  is  usually  referred 
to  as  a  standard  for  determining  the  other  values  for  the  other  ele- 
ments, is  set  down  as  the  fraction  of  a  gram  as  equivalent  to  one 
coulomb,  thus:  0.0011193  gram.  The  atomic  weight  of  silver  in 
terms  of  oxygen  =  16  is  107.93.  In  order  to  separate  a  gram- 
atomic  weight  of  silver  it  will  require,  using  W.  and  F.  Kohlrausch's 
mean  of  .0011181, 

: — £—  =  96,530  coulombs  of  electricity. 

This  number  of  coulombs,  96,530,  as  will  be  seen,  will  separate 
the  gram-atomic  weight  of  any  univalent  body,  and  is  sometimes 
called  the  electrochemical  equivalent  of  electricity.  The  fact  may 
be  stated  thus: 

One  chemical  equivalent  of  any  electrolyte  expressed  in  grams  re- 
quires the  passage  of  96,530  coulombs  for  its  liberation  or  electrolysis; 
96,530  coulombs,  therefore,  are  capable  of  liberating  the  chemical 
equivalent  of  any  electrolyte. 

This  is  an  exceedingly  important  constant  for  us  to  remember 
in  our  practical  work.  This  number  varies  in  value  a  trifle  accord- 
ing to  different  investigators,  and  will  be  encountered  as  96,540, 
etc.  In  the  table  opposite  the  chemical  equivalents  of  some  of 
the  most  important  elements  are  given.  The  student  must  not 
confound  a  chemical  equivalent  with  an  electrochemical  equivalent. 
These  terms  must  be  clearly  separated  in  his  mind  or  else  he  will 
be  continually  getting  into  confusion.  A  chemical  equivalent  is 
simply  the  atomic  weight  of  a  substance  divided  by  its  valence.  The 
atomic  weight  of  oxygen  being  16,  and  its  valence  2,  the  chemical 
equivalent  of  oxygen  would  be  8.  Oxygen  =  16.  Chemical  equiva- 
lent 16-7-2=8. 

In  the  table  on  page  84  the  electrochemical  equivalents  of  some 
of  the  most  important  elements  are  given.  By  dividing  the  atomic 
weight  in  the  second  column  by  the  valence  in  the  third  column, 
the  chemical  equivalent  given  in  the  fourth  column  is  obtained, 
and  this  number  multiplied  by  the  electrochemical  equivalent  of 
hydrogen  in  micrograms  per  coulomb  gives  the  electrochemical 
equivalent  of  the  ion  in  the  fifth  column,  also  in  micrograms  per 
coulomb.  The  numbers  in  the  sixth  column  are  the  reciprocals  of 


FARADAY'S  LAW. 
CHEMICAL    EQUIVALENTS    OF    CERTAIN    ELEMENTS. 


Element. 

A.  W. 

i 

C.  E. 

Element. 

A.  W. 

C.  E. 

Al"' 

27.1 

901 

Pb"         

206.9 

IO3   4.? 

Ba" 

3  valence 
1,17-4 

67  8 

Li 

2  valence 
7-03 

7O3 

Br 

2 
79.96 

7O    06 

Ms" 

i 
24.36 

•uo 

12     l8 

Cd"          

.       I 
II2.4 

<6    2 

Mn"  

2 

55 

27.  C 

Ca" 

2 
40.1 

20  o^ 

Hg 

2 
203-3 

2O  3     3 

Cl  

2 

35-45 

•JC     AC 

He".    . 

I 
203.3 

TOO  .  15 

Cr" 

i 
52.1 

26  o^ 

N'" 

2 
14.01 

A     6? 

Cu  

2 
63.6 

63  6 

Ni"  

3 

58.7 

20    3^ 

Cu" 

I 
63.6 

3i  8 

O" 

2 

16 

8  oo 

F  

2 
19 

10    OO 

K  

2 
39-15 

•2Q.  1C 

Au  

I 
197.2 

6e   77 

Ag 

I 
107-93 

IO7   O1? 

H  

3 
1.008 

i  008 

Na  

I 
23-05 

27    o< 

I  

i 
126.8:; 

126  85 

Sn"" 

I 
119 

26   7S 

Fe" 

i 
55-9 

Sr" 

4 
87.6 

A?  8 

Fe'"  

2 

55-9 

-/*yo 

18  63 

Zn" 

2 
65.4 

32    7 

3 

2 

1 

o-^  •  / 

those  in  the  fifth  given  in  grams.  The  electrochem'cal  equiva- 
lents of  compound  ions,  such,  for  example,  as  the  univalent  radical 
hydroxile  OH  and  the  bivalent  radical  SO 4,  are  similarly  obtained, 
the  chemical  equivalent  of  such  a  radical  being  the  sum  of  its  com- 
p  nent  atomic  masses  div  ded  by  its  valence. 

This  table  brings  out  the  beautiful  tru  h  of  Faraday's  law,  and 
forcibly  indicates  the  great  value  of  the  facts  he  was  able  to  point 
out  as  a  result  of  his  famous  investigations.  Let  us  experimentally 
test  Faraday's  law  in  the  laboratory  and  put  down  our  results.  For 
this  purpose  we  will  set  up  a  piece  of  apparatus  with  five  different 


EXPERIMENTAL   ELECTROCHEMISTRY. 


electrolytes  in  series  and  weigh  the  cathode  products  liberated  by 
the  same  current-flow. 

TABLE     SHOWING     RELATIVE     WEIGHTS     OF     BODIES     LIBERATED     BY 
A   COMMON   ELECTRIC    CURRENT. 


Element. 

Atomic 
Mass. 

Valence. 

Chemical 
Equivalent. 

Electrochemical  Equivalents 

Micro- 
grams  per 
Coulomb. 

Coulombs 
per 
Gram. 

ISt 

Hydrogen  

ad 
I 
15.96 

35-37 
14.01 
27.04 
206.40 
64.88 
58.60 
199.80 
199.80 
63.18 
63.18 
107.70 
196.2 

3d 

I 
2 

I 

3 

3 

2 
2 
2 

2 

I 
2 

I 
I 

3 

4th 
I 
7.98 

35-37 
4.67 
9.01 
103.20 
32.44 
39-3° 
99.90 
199.80 

3i-59 
63.18 
107.70 
65.40 

5th 
10.38 
82.83 
367.10 
48.47 
93-5C 
1071  .00 

336.70 

304  .  20 
1037.00 
2074.00 
327.90 
655.80 
IIlS.OO 
678.90 

6th 
96,340 
12,070 
2,724 
20,630 
10,700 

933-7 
2,970 
3,287 

964-3 
482.2 
3,050 
i,525 
894-5 
1,473 

Oxygen  

Chlorine 

Nitrogen 

Aluminium 

Lead  
Zinc  

Nickel 

^Mercury 

^Mercury 

CoDDer 

Copper  
Silver 

Gold  

EXPERIMENTAL   DEMONSTRATION   OF    FARAD  AY5  S   LAW. 

Referring  to  Fig.  39,  we  have  at  the  left  a  Hoffmann  apparatus, 
A,  for  the  electrolysis  of  solutions  yielding  gaseous  products  at  the 
electrodes.  The  gases  libe  ated  es  ape  into  the  two  tubes  and 
press  the  solution  up  into  the  reservoir  by  the  central  tube.  By 
opening  the  stopcocks  at  the  tops  of  the  two  side  tubes  containing 
the  gases,  the  weight  of  the  solution  in  the  reservoir  will  force  the 
gases  out,  when  they  may  be  collected  in  a  most  convenient  man- 
ner. Hydrogen,  for  example,  may  be  burned  as  a  jet,  after  electro- 
lyzing  a  dilute  solution  of  sulphuric  acid,  or  as  we  learned  in  the 
first  chapter,  by  electrolyzing  a  solution  of  potassium  or  sodium 
hydroxide.  Oxygen  and  hydrogen  will  be  liberated  in  such  a  piece 
of  apparatus  in  the  ratio  of  two  volumes  of  hydrogen  to  one  volume 
of  oxygen  whether  we  use  dilute  ulphuric  acid,  or  a  sodium,  or 
potassium-hydroxide  solution.  For  the  present  demonstration  of 
the  law  of  Faraday,  we  will  fill  the  Hoffmann  apparatus  with  a 
dilute  solution  of  sulphuric  acid  in  distilled  water  in  the  propor- 


FARADAY'S   LAW. 


tion  of  about  i  to  10.  In  the  cell  B  we  will  place  a  concentrated 
neutral  solution  of  silver  nitrate  in  distilled  water.  In  the  cell  C 
we  will  place  a  solution  of  cuprous  chloride,  which  may  be  made  by 
dissolving  a  few  grams  of  the  salt  in  hydrochloric  acid  after 
having  washed  it  carefully  on  a  filter  paper  with  warm  distilled 
water.  In  the  cell  D  we  will  place  an  electrolyte  consisting  of  cop- 
per sulphate  slightly  acidulated  with  nitric  acid.  In  the  cell  E 
we  will  use  a  solution  of  stannic  chloride,  best  prepared  in  the  fol- 


-.:-. 


FIG.  39. — Simple  Apparatus  for  Experimentally  Demonstrating  Faraday's  Law. 
A,  Hoffmann  apparatus;  B,  C,  D,  and  E,  cells  containing  electrolytes  and  elec- 
trodes; F,  delicate  ammeter. 

lowing  manner:  Take  of  stannous-chloride  crystals  1000  grams; 
hydrochloric  acid,  specific  gravity  1.125,  1170  cubic  centimeters; 
nitric  acid,  specific  gravity  1.220,  435  cubic  centimeters;  and  dis- 
tilled water  1000  cubic  centimeters.  Put  the  stannous  chloride  into 
a  1 2 -inch  evaporating-dish  and  add  the  1170  cubic  centimeters 
of  hydrochloric  acid;  warm  on  the  steam-bath  and  stir  until  the 
salt  is  dissolved;  then  dilute  with  one  liter  of  hot  water.  If  the 
solution  does  not  remain  clear,  there  is  a  deficiency  of  hydrochloric 
acid,  in  which  case  add  very  concentrated  hydrochloric  acid,  a 
few  drops  at  a  time,  until  the  solution  becomes  clear.  Add  the 
nitric  acid,  a  few  cubic  centimeters  at  a  time,  to  the  warm  solu- 
tion, stirring  well  after  each  addition.  After  a  considerable  part  of 
the  nitric  acid  has  been  added,  test  a  few  drops  of  the  solution  with 
a  drop  of  mercuric-chloride  solution.  If  a  white  precipitate  falls, 


86  EXPERIMENTAL   ELECTROCHEMISTRY. 

stannous  chloride  is  present,  and  more  nitric  acid  is  needed.  When 
no  white  precipitate  falls,  the  oxidation  is  complete,  and  no  more 
nitric  acid  should  be  added.  Put  the  liquid  product  into  a  tightly 
stoppered  bottle.  The  cathodes  of  all  the  cells  are  to  be  of 
platinum,  but  we  must  have  a  silver  anode  in  the  silver-nitrate 
solution  and  copper  anodes  in  both  of  the  copper  solutions.  The 
anode  in  the  tin  solution  may  be  of  platinum.  It  is  needless 
to  say  that  both  of  the  electrodes  in  the  Hoffmann  apparatus  are 
of  platinum.  These  five  electrolytes  are  now  all  connected  in  series 
with  a  delicate  ammeter,  as  shown,  and  the  terminal  wires  run  to 
a  storage-battery  or  such  a  motor-generator  as  described  in  the 
first  chapter.  The  electrolysis  may  be  allowed  to  proceed  for  any 
length  of  time  within  the  capacity  of  the  Hoffmann  apparatus. 
The  longer  the  run  the  better,  the  errors  in  weighing  a  decided 
increase  in  the  respective  cathodes  being  less  than  in  weighing  a 
slight  increase.  In  this  system  we  will  have  hydrogen  liberated, 
the  monovalent  element  silver,  the  monovalent  copper,  the  divalent 
copper,  and  the  tetravalent  tin.  If  the  experiment  has  been 
conducted  without  error  and  losses,  we  will  have  for  each  gram  of 
hydrogen  liberated  107.93  grams  of  silver,  63.6  grams  of  copper 
in  our  monovalent  copper  electrolyte,  31.8  grams  of  copper  in  our 
divalent  copper  solution,  and  26.75  gramms  of  tin  from  the  tin 
solution.  The  following  table  shows  the  result  of  a  carefully  con- 
ducted experiment  with  the  five  electrolytes  described  above: 


"108-38-^'-     63-5g'Cu''     3'.4Sg.Cu".     28.29g.Sn"«. 
Atomic  weight  .......      107.93  63.6  63.6  119.00 

Here  we  can  see  that  the  monovalent  elements  separate  in  pro- 
portion to  their  atomic  masses,  the  divalent  elements  in  propor- 
tion to  their  atomic  masses  divided  by  two,  the  tetravalent  element 
in  proportion  to  its  atomic  mass  divided  by  four.  The  beauty  of 
this  law  is  very  striking,  and  it  may  be  said  that  Faraday's  law 
knows  no  exceptions.  There  can  be  no  electrolytic  conduction 
without  the  corresponding  setting  free  of  substances  in  the  ratios  of 
their  chemical  equivalents.  As  we  shall  see  presently,  we  have 
ample  proof  of  moving  particles,  or  an  actual  mechanical  transfer 
of  matter  when  an  electric  current  is  passed  through  an  electrolyte. 
In  view  of  the  mechanical  transfer  of  matter,  experiments  were  con- 


FARADAY'S   LAW. 


ducted  upon  electrolytes  under  heavy  pressure  to  learn  if  Faraday's 
law  held  true  under  such  conditions.  At  first  it  was  noted  that 
the  electrical  conductivity  was  increased.  In  other  words,  more  cur- 
rent passed  through  the  electrolyte  than  was  accounted  for  by  weighing 
the  cathodes.  As  a  matter  of  fact  the  method  of  conducting  the 
experiment  was  faulty.  The  pressure  was  put  upon  the  electrolyte 
by  air,  some  of  which  was  of  course  forced  into  solution,  and  ionizing 
carried  a  portion  of  the  electric  current.  Professors  Nernst  and  Ostwald, 
in  Germany,  tested  Faraday's  law  most  critically  by  electrolyzing 
solutions  with  exceedingly  feeble  currents  to  see  if  any  electricity  at 
all  was  conducted  without  corresponding  quantitative  decomposition 
of  the  electrolyte.  In  one  experiment  upon  dilute  sulphuric  acid 
they  caused  an  exceedingly  small  amount  of  electricity  to  pass — only 
0.000005  coulomb.  They  determined  the  minute  quantity  of  gas 
set  free  and  found  that  Faraday's  law  held  even  for  such  a  small 
electric  current.  In  the  large  commercial  electrolytic  copper  refiner- 
ies the  law  has  been  tested  upon  enormous  scales  by  the  passage  of 
millions  of  coulombs  and  found  to  hold  absolutely.  The  law  of 
Faraday  in  the  light  of  the  many  attacks  and  investigations  upon  it 
seems  to  be  one  of  the  very  few  in  chemical  and  physical  science  which 
have  stood  throughout  without  suffering  exception  of  any  kind. 
We  have  now  learned  that  chemical  equivalent  quantities  of  all  ions 
have  the  same  capacity  for  electricity.  It  is  a  striking  and  interesting 
fact  to  note  that  this  is  analogous  to  the  law  of  Dulong  and  Petit, 
which  states  that  all  atoms  have  the  same  capacity  for  heat.  If  we 
multiply  the  atomic  weights  of  the  elements  by  their  specific  heats  we 
obtain  almost  a  constant,  which  number  we  term  atomic  heat.  The 
following  table  containing  a  few  elements  for  the  purpose  of  illustra- 
tion is  of  interest  here. 


Element. 

A., 
Atomic 
Weight. 

S-, 
Specific 
Heat. 

A.XS.t 
Atomic 
Heat. 

Potassium  

•2Q 

1  66 

6  c 

Calcium 

u-o 
ft  R 

^Manganese 

r  r 

.  1  /<J 

fi     >7 

Tin  

118 

J«7 

6   t 

Gold  

IO7 

O32 

2'5 

6     2 

Mercury  

2OO 

O32 

u-o 

6    A 

Lead         

2O7 

6     A 

Bismuth  

2OQ 

•uol 

0.4 
f.   , 

Silver  

1  08 

°-3 
6  o 

88 


EXPERIMENTAL   ELECTROCHEMISTRY. 


To  this  law  there  are  some  exceptions,  but  in  the  majority  of 
cases  we  have  practically  a  constant. 

VOLTAMETERS. 
METAL  AND   GAS   TYPE.      THE   SILVER  VOLTAMETER. 

The  most  accurate  instrument  for  measuring  current-flow  is 
without  question  the  silver  voltameter,  and  is  at  the  same  time  the 
most  easily  constructed. 

Fig.  40  will  make  the  arrangement  clear.  Two  comparatively 
heavy  plates  of  pure  silver  are  joined  together  to  make  one  electrode, 
between  which  a  thin  silver  sheet  forming  the  other  electrode  is 
suspended.  In  the  silver  voltameter  the  very  high  equivalent  of 


FIG.  40. — Construction  of  Silver  Voltameter  for  the  Measurement  of  Current-flow  in 
Coulombs.     A,  top  view  looking  down  into  cell;   J3,  end  view;  C,  side  view. 

silver,  and  consequently  the  great  mass  isolated  upon  the  cathode  by 
comparatively  feeble  currente,  reduce  the  errors  in  weighing  to  a 
minimum.  There  is  one  disadvantage  in  the  use  of  the  silver  voltam- 
eter, however,  and  this  is  due  to  the  fact  that  silver  tends  to  precipi- 
tate out  upon  the  cathode  in  crystalline  form,  and  if  the  electrolyzing 
current  is  strong,  some  of  the  crystals  form  so  quickly  that  they  will 
drop  ofl  and  introduce  errors  from  this  cause.  The  electrolyte  for 
this  instrument  is  of  a  concentrated  neutral  silver-nitrate  solution. 
With  such  an  instrument  a  current  of  one  ampere  deposits  upon  the 
thin  silver  cathode 

0.0011181  gram  silver  per  second, 

or  0.067086  gram  silver  per  minute, 

or  4.025160  grams  silver  per  hour. 


FARADAY'S  LAW.  89 

With  such  an  instrument  in  series  with  an  electric  current,  by 
determining  the  weight  of  the  cathode  before  and  after  the  run  we 
are  in  a  position  to  calculate  the  number  of  coulombs  that  have 
passed  through  the  system.  If  we  had  an  absolutely  steady  current 
we  could  get  at  the  same  thing  by  putting  a  correct  ammeter  in  series 
and  multiplying  the  amperes  indicated  by  the  number  of  seconds 
during  which  the  current  passed  and  get  the  coulombs  used.  If  the 
strength  of  the  current  varied,  however,  this  plan  would  be  worthless. 
With  voltameters  of  either  the  metal  or  gas  type  the  current  may 
vary,  flowing  at  very  different  rates  in  a  given  time,  but  the  increase 
in  weight  of  the  cathode  will  give  the  true  number  of  coulombs 
regardless  of  such  fluctuations. 

THE   COPPER   VOLTAMETER. 

Here  we  have  a  similar  construction,  only  with  plates  of  pure 
copper  instead  of  silver  ones.  The  electrolyte  consists  of  a  solu- 
tion of  30  grams  of  crystallized  chemically  pure  copper  sulphate 
dissolved  in  200  grams  of  distilled  water,  to  which  5  grams  of 
chemically  pure  concentrated  sulphuric  acid  is  added  and  5  cubic 
centimeters  of  ethyl  alcohol.  Such  an  instrument  is  inexpensive  and 
is  adapted  to  the  most  general  requirements.  The  copper  voltameter 
can  be  left  in  circuit  with  work  through  great  lengths  of  time  without 
fear  of  losing  any  copper  by  falling  from  the  cathode.  The  copper 
will  be  deposited  upon  the  cathode  as  a  beautiful,  salmon-pink 
metal.  Such  an  instrument  will  answer  every  purpose  as  an  ampere- 
hour  meter  for  heavy  work  if  the  plates  are  made  generous  enough 
in  area.  With  this  voltameter  a  current  of  one  ampere  deposits 
upon  the  thin  copper  cathode  . 

0.00033  gram  of  copper  per  second, 
or  0.01980  gram  of  copper  per  minute, 

or  1.18800  grams  of  copper  per  hour. 

This  will  be  found  the  most  satisfactory  instrument  for  general 
work  and  every  student  in  practical  electrochemistry  should  set  one 
up  for  his  current  measurements.  With  very  small  currents,  how- 
ever, there  is  apt  to  be  a  slight  error  introduced  with  the  use  of  the 
copper  voltameter  because  of  some  cuprous  oxide  being  deposited 


90  EXPERIMENTAL   ELECTROCHEMISTRY. 

along  with  the  copper.  If  we  have  at  least  o.i  of  an  ampere 
following  through  the  instrument,  and  its  cathode  area  is  at  least 
100  square  centimeters,  there  will  be  no  trouble  from  this  cause, 
especially  when  the  electrolyte  contains  the  sulphuric  acid  and 
alcohol  as  given  in  the  above  formula. 

THE   GAS-VOLTAMETER. 

In  this  instrument  either  dilute  sulphuric  acid  or  a  solution  of 
potassium  or  sodium  hydroxide  may  be  used  and  the  mixed  oxygen 
and  hydrogen  gases  determined  by  volume.  Dilute  sulphuric  acid 
is  perhaps  the  best  for  the  purpose,  and  should  be  mixed  in  the 
proportion  of  one  part  of  strong  sulphuric  acid  to  ten  or  twelve 
parts  of  distilled  water.  The  acidulated  water  is  decomposed 
between  two  platinum  plates  and  gas  collected  and  reduced  to  o° 
and  760  millimeters  by  the  well-known  formula  for  reducing 
gases  to  a  standard  for  comparison.  This  type  of  voltameter, 
as  illustrated  in  Fig.  41,  is  very  convenient  because  it  does 


FlG.  41. — Approved  Form  of  Gas  Voltameter  for  the  Measurement  of  Current-flow 
in  Coulombs.  The  student  must  not  confound  the  word  voltameter  with  the 
word  voltmeter. 

away  with  all  weighings.  The  volume  can  be  read,  and  by  means 
of  tables,  when  the  temperature  has  been  taken,  the  gas  volume 
can  be  quickly  reduced  to  a  standard.  This  instrument  is  not 
quite  as  accurate  as  the  copper  voltameter,  and,  moreover,  requires 
about  two  volts  of  electrical  pressure  to  drive  a  current  through 
it.  If  we  are  using  a  storage-battery  or  the  motor-generator  we 


FARADAY'S   LAW.  91 

must  take  into  consideration  the  two  volts  required  by  such  a  volt- 
ameter in  making  any  calculations.  To  use  the  voltameter  the  water 
in  the  vertical  measuring-tube  should  first  be  saturated  with  oxy- 
hydrogen gas,  by  allowing  it  to  fill  about  half  full,  and  then  discon- 
necting and  shaking,  with  the  thumb  or  a  stopper  closing  the  end  of 
the  tube.  With  this  type  of  instrument  an  ampere  flowing  liberates 

0.1740  cc.  of  oxyhydrogen  gas  per  second, 
or  10.4400  cc.  of  oxyhydrogen  gas  per  minute, 

or  626.4000  cc.  of  oxyhydrogen  gas  per  hour. 

The  above  volumes  are  at  o°  and  760  millimeters  pressure.  The 
vertical  tube  for  collecting  the  gas  is  best  graduated  direct  into  cubic 
centimeters,  reading  to  tenths.  Such  a  gas-voltameter  must  be 
ordered  from  one  of  the  chemical  supply  houses  unless  the  student 
is  an  expert  glass-blower,  but  one  answering  every  requirement  can 
be  quickly  made  in  the  laboratory  without  the  art  of  glass-blowing, 
as  illustrated  at  A  in  Fig.  42.  Here  we  have  a  glass  cylinder  fitted 


FlG.  42. — Gas-voltameter  and  Large  Collecting-jar  in  Series  with  Three  Electrolytic 
Cells  equipped  with  Voltmeters.  A,  easily  constructed  gas-voltameter;  B,  col- 
lecting-jar; C,  D,  and  E,  electrolytic  cells  with  voltmeters  for  determining  the 
electrical  energy  expended  in  each  electrolyte. 

with  a  tight  stopper  (the  whole  success  of  the  apparatus  depends 
upon  its  being  tight),  containing  two  concentric  platinum  cylinders, 
one  forming  the  anode  and  the  other  the  cathode.  The  large  bell 
jar,  B,  allows  of  a  long  run  before  it  is  necessary  to  stop  and  measure 
the  gas  volume.  The  bell  jar  may  be  graduated  and  its  readings 
taken  for  rough  work,  but  for  close  work  the  gas  must  be  transferred 
to  a  more  delicate  graduate  and  reduced  to  standard  conditions. 


92  EXPERIMENTAL  ELECTROCHEMISTRY. 

Now  we  have  just  learned  that  the  same  current  will  deposit 
upon  the  cathodes  of  electrolytic  cells  in  series  chemical  equivalents 
of  the  elements  as  well  as  chemical  equivalents  of  compound  ions. 
Chemical  equivalents  of  all  bodies  are  therefore  liberated  or  deposited 
by  the  same  current.  Is  the  absorption  oj  energy  the  same  in  these 
different  cases?  It  is  not,  and  the  experiment  illustrated  in  Fig.  42 
has  been  designed  by  the  writer  to  bring  out  this  most  important 
point.  Let  us  place  three  different  electrolytes  in  the  cells  C,  D,  and 
E,  and  connect  across  the  electrodes  in  each  case  a  delicate  voltmeter 
to  indicate  the  fall  of  potential  in  each  cell.  Although  the  coulombs 
passed  will  of  course  be  equal  in  each  cell,  because  they  are  in  series, 
and  the  metals  will  be  deposited  in  the  ratio  of  their  chemical  equiva- 
lents, the  number  of  joules  expended  in  each  cell  will  be  different. 
Those  who  have  studied  electricity  will  know  that  the  joule  is  the 
unit  of  electrical  energy,  and  is  the  product  of  the  ampere  by  the 
second,  by  the  volt.  As  a  coulomb  is  the  product  of  an  ampere 
by  a  second,  we  may  say  that  the  joule  is  the  product  of  a  coulomb 
by  a  volt.  It  is  not  the  intention  of  the  author  to  go  into  the  reason 
for  unequal  absorptions  of  energy  in  different  electrolytes  until  the 
next  chapter,  when  the  matter  will  be  fully  dealt  with.  It  is,  however, 
the  wish  of  the  writer  to  impress  upon  the  student  that  there  is  a 
difference,  and  that  its  explanation,  as  will  be  learned  later,  is  in 
accordance  with  the  doctrine  of  conservation  of  energy,  and  a'  point 
of  great  beauty  in  electrochemistry.  With  an  arrangement  of  appara- 
tus as  indicated  in  Fig.  42,  therefore,  we  would  be  able  to  calculate 
by  means  of  the  gas-voltameter  in  series,  the  number  of  coulombs 
which  have  passed  through  the  system,  and  by  the  respective  readings 
of  the  voltmeters  across  the  electrodes  of  the  respective  cells  we 
would  be  able  to  determine  the  amount  of  energy  absorbed  in  each. 
So  much  upon  this  point  for  the  present.  It  was  stated  that  we 
should  have  introduced  in  connection  with  Faraday's  law,  experi- 
mental evidence  proving  that  the  passage  of  an  electric  current 
through  an  electrolyte  was  accompanied  by  an  actual  mechanical 
transfer  of  matter.  A  very  simple  and  a  very  beautiful  experiment 
may  be  quickly  performed  which  goes  to  show  the  transport  of 
ponderable  material.  Arrange  a  large  U  tube,  as  illustrated  in 
Fig.  43,  with  stoppers  and  platinum  electrodes.  Through  one 
stopper  bore  a  small  hole  to  receive  a  bent  glass  tube  as  shown. 


FARADAY'S  LAW. 


93 


Prepare  a  concentrated  solution  of  zinc  chloride  in  distilled  water  to 
serve  as  the  electrolyte.  Arrange  the  tube  in  series  with  the  lamp- 
bank  and  electric-lighting  circuit  as  described  in  Chapter  I,  and 
throw  in  one  or  two  lamps.  The  zinc  will  immediately  begin  to 
grow  in  the  form  of  a  beautiful  metallic  tree  and  chlorine  may  be  de- 
tected issuing  from  the  bent  glass  tube  over  the  opposite  pole.  There 
is  optical  evidence  that  we  have  an  accumulation 
of  metal  at  the  cathode,  and  evidence  of  an 
equally  striking  nature  that  we  have  chlorine  at 
the  anode.  In  the  drawing,  the  bleaching  action 
is  shown  upon  a  piece  of  calico.  What  is  taking 
place  at  the  bend  in  the  bottom  of  the  tube, 
however  ?  Have  we  mechanical  movement  there  ? 
We  have  been  led  to  believe  that  we  have 
chlorine  ions  moving  in  one  direction  and  zinc 
ions  moving  in  the  other.  Is  it  true,  and  is  there 
any  experiment  to  prove  it?  The  author  has 
designed  three  to  furnish  evidence  in  support 
of  this,  and  they  are  here  published  for  the 
first  time  in  book  form.  The  first  of  the  three 
experiments  is  illustrated  in  Fig.  44.  Although 
glass  is  always  stated  to  be  the  best  elec- 
trical insulator  known,  it  occurred  to  the 
writer  that  its  constituents  'could  carry  the 
electric  current  if  the  ions  were  only  free  to  migrate.  In  other 
words,  glass  was  regarded  by  the  writer  as  being  a  solid  elec- 
trolyte. Ordinary  glass,  as  is  well  known  to  the  general  chemist •, 
consists  of  silicon  dioxide  fused  with  calcium  and  sodium  carbonate. 
Ordinary  glass  is  therefore  a  soda  lime,  silicon-dioxide  glass.  Bohe- 
mian glass  is  made  with  potassium  carbonate,  and  flint  glass  is  made 
by  melting  together  lead  oxide,  potassium  carbonate,  and  silicon 
dioxide,  while  strass  is  a  species  of  glass  very  rich  in  lead.  We  have, 
as  may  be  seen,  all  the  ions  necessary  to  carry  electric  currents  if  they 
were  only  free  to  move  about.  To  test  this  point  little  rods  of  solid 
glass  of  the  different  varieties  were  softened  and  platinum  wires 
run  into  the  ends  to  a  distance  of  about  a  centimeter.  The  rods 
were  cut  a"bout  3  centimeters  long,  so  there  was  in  each  case  an  "  insu- 
lating gap"  ctf  about  a  centimeter  between  the  ends  of  the  platinum 


Mechanical  Trans- 
port of  Matter. 

FIG.  43. — Electrol- 
ysis of  a  Solution  of 
Chloride  of  Zinc, 
showing  the  rapid 
growth  of  a  "zinc- 
tree"  and  the  libera- 
tion of  chlorine  as 
indicated  by  its 
bleaching  action. 


94 


EXPERIMENTAL   ELECTROCHEMISTRY. 


wires.  A  glance  at  the  figure  shows  such  a  glass  rod  with  the  plati- 
num wires  at  B.  A  delicate  milliammeter  is  joined  in  series  with  the 
platinum  wires  and  our  lamp-bank  (not  shown  in  the  illustration), 
and  of  course  no  deflection  is  shown  upon  the  indicating  instrument 
because  glass  is  an  insulator  when  cold.  Now  bring  a  Bunsen 
burner,  A,  under  the  glass  rod  and  heat  it  up  gradually.  As  the 
glass  begins  to  soften  and  flow,  the  milliammeter  begins  to  show  con- 
ductivity. With  the  softening  of  the  glass,  therefore,  the  ions  are  free 
to  travel.  This  is  a  very  pretty  and  convincing  experiment  when 
performed  with  a  large-scale  ammeter  so  that  in  a  lecture-room  an 
entire  class  may  see  the  deflection  of  the  needle.  It  is  of  interest 


FIG.  44. — Simple  and  Easily  Performed  Experiment  to  Show  Mechanical  Transfer 
of  Matter  through  Solid  Glass.  A,  Bunsen  burner;  B,  solid  rod  of  glass;  C, 
milliammeter  to  show  conduction  of  the  electric  current. 

at  this  time  to  point  out  the  fact  that  all  electrolytes  when  in  solution 
in  water  conduct  better  when  heated  up^  This  is  just  the  reverse 
with  metals  and  alloys. 


EXPERIMENTS   WITH   FROZEN   ELECTROLYTES. 

What  will  be  the  effect  upon  the  movement  of  ions  on  freezing  an 
electrolyte?  This  question  presented  itself  to  the  writer,  and  not 
coming  across  records  of  any  experiments  with  frozen  electrolytes, 
or  any  theoretical  discussion  of  the  same,  it  was  decided  to  investigate 
the  matter  experimentally.  According  to  our  ionic  migration,  or 
convection  theory  of  electricity  through  substances  in  solution,  the 
conductivity  of  an  electrolyte  should  cease  or  approach  zero  value 


FARADAY'S   LAW. 


95 


when  frozen.  When  the  medium  containing  the  ions  is  frozen 
solid  will  the  conductivity  actually  cease  ?  Will  the  ions  move  freely 
through  as  before,  or  can  they  be  forced  through  at  diminished 
velocity?  The  writer  has  made  numerous  experiments  upon  the 
physical  properties  of  ice,  and  has  found  it  to  be  viscous-like  in 
behavior.  This  property  has  also  been  demonstrated  by  Profes- 
sors Tyndall  and  Agassiz  upon  a  tremendous  scale  in  their  studies 
of  the  Swiss  glaciers.  Ice  can  be  bent,  twisted,  and  pressed 
into  molds,  and  be  made  to  flow  under  pressure  like  semi-molten 
glass.  The  ions  in  a  frozen  electrolyte,  therefore,  should  be  in  a 
measure  free  to  move  slowly  when  subjected  to  an  electric  current. 
Let  us  look  into  the  facts  of  actual  experiments.  Figc  45  shows  a 


FIG.  45. — Experiment  \vith  Frozen  Electrolytes.  The"V"  tube  at  the  left  of  the 
drawing  contains  the  solution  to  be  frozen  and  is  immersed  in  a  beaker  contain- 
ing the  freezing-mixture.  Indicating  galvanometer  in  the  center,  storage-battery 
at  right.  Three  cells  of  battery  at  least  are  necessary  in  this  experiment  or  else 
the  lamp-bank  shown  in  Chapter  I. 

simple  arrangement  for  experimenting  with  frozen  electrolytes. 
The  following  experimental  work  embraced  the  freezing  of  a  dozen 
or  more  solutions,  including  NaCl,  KC1,  HC1,  H2SO4,  K2Cr2O7, 
KI,  etc.,  and  in  every  instance,  with  an  ordinary  ammeter  in  series, 
the  current  appeared  to  be  completely  stopped  when  the  solvent  con- 
taining the  ions  was  solidified.  The  temperature  in  each  case  was 
well  below  the  freezing-point,  the  solutions  frozen  being  very  dilute 
not  only  for  the  sake  of  complete  dissociation  of  the  salts,  but  for  the 
comparative  ease  with  which  they  could  be  frozen.  The  freezing- 
mixtures  consisted  of  pounded  ice  and  salt  and  also  the  well-known 


96  EXPERIMENTAL   ELECTROCHEMISTRY. 

mixture  of  sodium  sulphate  6  parts,  ammonium  nitrate  5  parts, 
dilute  nitric  acid  5  parts.  The  lowest  temperature  attained  by 
the  use  of  this  mixture  was  —30°  C.,  which  was  more  than  ample  to 
freeze  any  of  the  above  dilute  solutions.  The  plan  of  conducting 
an  experiment  which  is  suitable  for  a  lecture-room  experiment  is 
shown  in  the  illustration  and  consists  of  a  V  tube  of  glass  fitted 
with  stoppers  and  platinum  electrodes,  which  may  be  immersed  in 
the  beaker  containing  the  freezing-mixture.  A  large  upright  galva- 
nometer is  shown  in  the  center  and  a  cell  of  storage  battery  at  the 
right.  One  cell  of  battery  is  rarely  sufficient  for  electrolysis,  as 
will'  be  learned  in  the  next  chapter  when  we  discuss  the  energy 
required  for  the  electrolysis  of  various  compounds,  and  at  least 
three  should  be  used  here.  Our  lamp-bank  is  well  suited  for 
this  experiment.  As  the  electrolyte  freezes  the  pointer  of  the 
ammeter  or  galvanometer  comes  to  zero  and  upon  thawing  again 
travels  over  the  scale.  Thus  we  get  no  deflection  with  an  ordi- 
nary ammeter  or  galvanometer  upon  freezing  a  solvent  con- 
taining ions,  even  when  the  lamp-bank  is  used,  and  we  have  a  differ- 
ence of  potential  of  no  volts  between  the  terminals  of  the  system. 
One  might  be  misled  in  stating  that  we  had  a  non-conductor  just  as 
one  is  accustomed  to  speak  of  glass.  On  going  a  step  further,  however, 
and  substituting  an  exceedingly  delicate  galvanometer  or  milliammeter 
a  good  deflection  through  the  frozen  electrolyte  is  at  once  obtained. 
Of  course  it  is  necessary  to  predetermine  the  freezing-points  of  the 
solutions  to  be  experimented  upon  and  to  be  sure  the  temperature 
is  well  below  that  required  to  insure  the  absence  of  any  liquid  elec- 
trolyte. The  slight  conductivity  can  only  be  explained  on  account 
of  the  viscous-like  behavior  of  ice.  If  ice  became  a  perfect  solid  it 
would  undoubtedly  become  a  perfect  non-conductor.  The  con- 
ductivities of  crystals  of  copper  sulphate,  iron  sulphate,  etc.,  were 
tried  and  proved  to  be  non-conductors  with  the  most  delicate  instru- 
ments, unless  fused,  when  they  of  course  conducted  as  usual.  A 
crystal  is  a  true  solid.  It  proves  to  be  a  true  non-conductor.  The 
passage  of  an  electric  current  through  chemical  bodies,  therefore, 
must  be  accompanied  by  the  mechanical  movement  of  matter. 
The  third  experiment  to  furnish  evidence  in  support  of  ion  transport 
is  dependent  upon  heat  convection  as  well  as  electrical  convection. 


FARADAY'S   LAW. 


97 


HEAT   CONVECTION  IN  ELECTROLYTIC   CONDUCTION. 

The  apparatus  illustrated  in  Fig.  46  was  designed  for  the  purpose 
of  indicating  the  movement  of  ponderable  material  of  which  ions 
are  composed,  through  the  agency  of  the  heat  which  they  may  be 
made  to  carry.  It  was  reasoned  that  if  we  actually  had  ponderable 
material  moving  through  an  electrolyte,  this  material  could  be  made 
to  convey  heat  as  well  as  electricity,  and  by  the  proper  design  of  an 
apparatus  the  method  could  be  employed  for  determining  the  absolute 


FIG.  46. — Apparatus  to  Show  Heat  Convection  in  Electrolytic  Conduction.  A  and  B 
are  calorimeters  made  from  muff  boxes  lined  with  heavy  hair-felt.  Beckmann 
thermometers  dip  into  "T"  connections  in  the  glass  tube  containing  the  elec- 
trolyte. 

velocities  of  ions,  although  in  a  rough  way,  because  of  sources  of 
error  difficult  to  overcome.  At  the  left  in  the  illustration  is  the  anode 
calorimeter,  A,  containing  a  T  joint  receiving  the  bulb  of  a  delicate 
thermometer.  About  this  T  joint  is  wound  a  little  coil  of  platinum 
wire  for  the  purpose  of  heating  the  contained  electrolyte.  This 
coil  is  attached  to  stout  copper  wires  terminating  in  binding-sleeves 
outside  the  calorimeter,  which  is  a  pasteboard  muff  box  lined  with 
hair-felt.  In  the  cathode  calorimeter  B  is  a  similar  T  tube  and 
thermometer,  but  without  the  heating-coil.  The  electrolyte  in  one 
experiment  consisted  of  dilute  sulphuric  acid  in  the  proportion  of 
20  cubic  centimeters  of  concentrated  sulphuric  acid  to  100  cubic 
centimeters  of  distilled  water.  The  thermometers  employed  read 


98  EXPERIMENTAL  ELECTROCHEMISTRY. 

from  o°  to  100°  C.  in  0.1°  divisions.  The  platinum  coil  was  con- 
nected to  the  no-volt  lighting  wires  through  a  finely  graduated 
variable  resistance,  allowing  of  a  very  close  control  of  current  and 
heating  effect.  The  following  is  an  account  of  an  experiment  con- 
ducted with  the  electrolyte  referred  to. 

The  anode  calorimeter  was  placed  upon  a  higher  level  than  the 
cathode  calorimeter  for  the  purpose  of  preventing  simple  convection 
currents  due  to  the  expansion  of  the  water  molecules  within  the  glass 
T  surrounded  by  the  heating  coil  traveling  by  displacement.  The 
experiment  was  started  by  allowing  o.i  ampere  to  flow  through 
the  apparatus,  with  a  potential  gradient  of  i  volt  per  centimeter. 
This  current  was  allowed  to  flow  for  three  hours,  when  the  mercury 
in  the  two  thermometers  appeared  to  reach  a  maximum  reading. 
It  should  be  stated,  however,  that  in  a  special  experiment  con- 
ducted purely  to  note  a  special  phenomenon  the  thermometers 
continued  to  show  a  rise  in  temperature,  although  at  an  ex- 
ceedingly low  rate,  even  after  three  hours,  it  being  found  that 
nine  and  one-half  hours  were  really  required  before  a  perfect 
balance  between  the  heat-energy  supply  and  the  heat-energy  radia- 
tion loss  through  the  calorimeters  was  reached.  The  rate  of  rise 
of  temperature  as  indicated  by  the  thermometers  at  the  end  of 
three  hours,  however,  was  so  low  as  to  allow  of  an  experimental 
determination  of  the  velocity  of  ionic  travel.  To  determine  the 
velocity  of  hydrogen  ions,  therefore,  it  is  only  necessary  to  replace 
the  ordinary  thermometer  in  the  cathode  calorimeter  by  an  open-scale 
Beckmann  thermometer  of  the  most  sensitive  type,  carefully  adjusted 
to  the  temperature  of  the  electrolyte  into  which  it  is  to  dip,  which  of 
course  may  be  done  from  the  reading  on  the  ordinary  thermometer. 
The  apparatus  is  then  allowed  to  stand  for  an  additional  hour  for 
the  new  thermometer  to  reach  a  perfect  equilibrium,  when  the  cur- 
rent is  admitted  to  the  platinum  heating-coil,  the  time  being  noted  at 
the  moment  of  closing  the  circuit.  In  another  separate  and  special 
experiment  the  electrolyte  in  the  T  tube  in  the  anode  calorimeter 
A  was  kept  at  90°  C.  for  three  hours  without  affecting  the  thermom- 
eter in  the  cathode  T  tube  but  0.2°  C.,  and  this  was  due  to  conduction 
through  the  glass,  and  possibly  a  little  convection  in  spite  of  the 
more  elevated  anode  calorimeter.  Water  conducts  itself,  to  a  slight 
extent,  so  this  error  must  be  learned  and  applied  as  a  correction.  It 


FARADAY'S   LAW.  99 

will  be  seen  that  this  glass  tube  is  inclosed  within  a  second  glass  tube 
with  an  air-space  around  it,  and  the  whole  thing  is  in  turn  inclosed 
in  a  jacket. of  hair-felt.  With  the  experiment  under  way  as  described 
it  only  remained  to  watch  for  the  first  indication  of  a  marked  rise 
upon  the  Beckmann  thermometer  in  the  cathode  calorimeter.  The 
distance  between  the  two  thermometer-bulbs  was  80  centimeters. 
The  hydrogen  ions  apparently  arrived  in  one  experiment  twenty 
minutes  late  according  to  calculations  as  to  when  they  were  due. 
This  tardiness  may  be  attributed  to  the  lack  of  sensitiveness  of  the 
thermometer.  Undoubtedly  the  ions  arrived  on  time,  if  the  phe- 
nomenon is  really  due  to  the  heat  which  they  carry,  but  it  remained 
for  an  accumulative  action  to  take  place  before  there  was  heat 
enough  to  affect  the  large  mass  of  mercury  in  the  thermometer.  A 
thermopile  and  galvanometer  would  have  acted  quicker.  So  much 
for  evidence  of  ion  migration  and  mechanical  movement.  We  are 
now  in  a  position  to  take  up  electrochemical  work  of  a  more  practical 
character  and  will  open  the  next  chapter  with  such  introduction. 


CHAPTER  VII. 

ENERGY  REQUIRED  IN  ELECTROLYSIS.  PRACTICAL  FORMULA 
FOR  COMPUTING.  ELECTROLYTIC  SEPARATION  OF  MET- 
ALS. THE  ROTATING  ANODE  IN  ELECTRO-ANALYSIS. 

IN  the  last  chapter  it  was  pointed  out  that  whereas  a  given  cur- 
rent flowing  for  a  given  time  would  separate  chemical  equivalents 
of  electrolytes,  the  energy  absorbed  in  electrolytes  of  different  con- 
stitutions was  not  the  same.  Now,  why  is  it  that  with  some  elec- 
trolytes more  energy  is  required  to  isolate  the  constituent  parts 
than  with  others?  We  have  learned  that  96,540  coulombs  will 
isolate  the  chemical  equivalent  of  any  electrolyte,  and  we  now  learn 
that  these  96,540  coulombs  must  be  supplied  at  different  electrical 
pressures  for  different  electrolytes.  The  96,540  coulombs  with- 
out an  electromotive  force  would  not  flow,  and  it  is  evident  that 
we  must  have  some  electromotive  force  in  order  to  have  electrical 
energy,  for  the  joule  which  is  the  unit  of  electrical  energy  is  the 
product  of  the  coulombs  by  the  volts  in  an  electrical  circuit.  We 
may  theoretically  have  any  amount  of  electrical  energy  we  may  wish 
by  multiplying  our  96,540  coulombs  by  volts  or  fractions  of  volts. 
To  determine  why  some  electrolytes  require  more  energy  (a  higher 
electrical  pressure  with  the  96,540  coulombs)  than  others,  we  need 
but  to  refer  to  the  "heats  of  formation"  of  different  electrolytes, 
and  the  doctrine  of  the  "conservation  and  correlation  of  energy." 
By  "heat  of  formation"  of  a  chemical  compound,  we  mean  the 
number  of  calories  liberated  (and  sometimes  absorbed)  when  one 
gram-molecule  of  the  substance  is  produced.  To  find  the  heat 
of  formation  of  a  chemical  compound,  a  gram-molecule  of  the 
substance  is  taken  and  its  combustion  in  oxygen  determined.  Ac- 
cording to  the  principle  discovered  by  Hess,  if  we  know  the  heat 
of  combustion  of  a  gram-molecule  of  a  compound,  we  may  de- 
termine its  heat  of  formation  by  subtracting  the  heat  of  combus- 

•  100 


ENERGY  REQUIRED   IN   ELECTROLYSIS.  IOI 

tion  of  the  compound  from  the  heats  of  combustion  of  the  constitu- 
ent elements.  For  example,  the  heat  of  formation  of  methane, 
CH4,  is  determined  by  measuring  the  heat  of  combustion  of  the 
compound  in  oxygen  in  a  suitable  calorimeter,  and  the  heats  of 
combustion  of  its  elements  in  the  same  manner,  and  subtracting 
one  from  the  other  as  follows: 

Heat  of  combustion  of  methane,  CH4,  =211,930  calories,  yielding 
CO2  and  2H2O. 

Heat  of  combustion  of  carbon,  0=96,960  calories,  yielding  CO2. 

Heat  of  combustion  of  hydrogen,  H4  =  136,720  calories,  yielding 
2H20. 

The  heat  of  formation  of  a  gram-molecule  of  methane  is 
found  by  subtracting  211,930  calories  (its  heat  of  combustion) 
from  96,960  +  136,720  calories  (the  heats  of  combustion  of  its  con- 
stituent parts)  as  given: 

96,960 
136,720 


233,680 
211,930 

21,750  calories  =  heat  of  formation  of  CH4. 

Therefore  when  the  gram-molecule  of  CH4  is  produced  a 
definite  amount  of  energy  is  liberated;  and  according  to  the  doctrine 
of  the  conservation  of  energy,  this  same  quantity  of  energy  must 
be  absorbed  again  before  the  compound  can  be  broken  up  into 
its  constituent  parts.  CH4  is  not  an  electrolyte;  the  compound 
was  taken  to  serve  as  an  illustration.  Below  we  have  tabulated 
the  heats  of  formation  of  a  number  of  chemical  compounds  taken 
from  the  general  tables  in  Ostwald's  "  Outlines  of  General  Chem- 
istry." These  have  been  converted  into  small  calories. 

There  are  of  course  many  others  given  in  a  comprehensive  table, 
including  both  organic  and  inorganic  compounds,  electrolytes  and 
non-electrolytes,  but  it  is  believed  that  the  list  given  includes  a 
sufficient  number  of  electrolytes  to  be  of  service  in  the  laboratory. 
With  such  a  table  of  heats  of  formation,  and  the  doctrine  of  the 
conservation  and  correlation  of  energy,  taken  in  connection  with 


102 


EXPERIMENTAL  ELECTROCHEMISTRY. 


Compounds. 

Formulas. 

Calories. 

Compounds. 

Formulas. 

Calories. 

Hydrochloric  acid.  .  .  . 

HC1 

22,000 

Ferric  chloride  

FeCl3 

06  100 

"\\fater                   

H2O 

68  4.00 

Ferrous  sulphate 

FeSO4 

23s  600 

Sulphuric  acid  

H2SO4 

IQ7  ,IOO 

Nickel  chloride.  .  . 

NiCl2 

74  s"oo 

Ammonia       

NH3 

12,000 

Nickel  sulphate  

NiSO4 

HNO3 

40  100 

Zinc  oxide 

ZnO 

3  r  goo 

Potassium  hydroxide  . 

KOH 
KC1 

103,200 
104.  300 

Zinc  chloride  
Zinc  bromide 

ZnCl2 
ZnBr2 

97,200 

Potassium  bromide  .  . 

KBr 

nc  100 

Zinc  iodide 

ZnI2 

Potassium  iodide.  .  .  . 
Potassium  nitrate.  .  . 
Sodium  hydroxide.  .  . 
Sodium  chloride  
Sodium  bromide  

KI 
KNO3 
KOH 
NaCl 
NaBr 
Nal 

80,100 
119,500 

101,900 

97,900 

85,800 

69  100 

Cadmium  chloride  .  . 
Cadmium  bromide.  . 
Cadmium  iodide.  .  .  . 
Cuprous  chloride.  .  . 
Cuprous  bromide  .  .  . 
Cuprous  iodide 

CdCl2 
CdBr2 
CdI2 
CuCl2 
CuBr2 
CuI2 

93,200 
75,200 
48,800 
51,600 
32,600 

•52   TOO 

Sodium  sulphate  
Sodium  hydrogen  sul- 

Na2S04 

328,800 

Cupric  sulphate.  .  .  . 
Cupric  nitrate.  .  . 

CuSO4 

Cu(NO3)2 

182,600 

82  300 

NaHSO4 

267  800 

M^ercurous  chloride 

Hg2Cl2 

62  600 

Ammonium  chloride. 
Ammonium  bromide. 

NH4C1 
NH4Br 

75,800 

6=5,400 

Mercuric  chloride.  .  . 
Silver  nitrate  

HgCl2 
AgNO3 

53,200 
28,700 

Ammonium  iodide  .  .  . 

NH4I 

40,300 

Lead  chloride  

PbCl2 

82,800 

Calcium  hvdroxide.  .  . 

Ca(OH)2 

214  900 

Lead  bromide 

PbBr2 

64  ?oo 

CaO 

131  ooo 

Lead  iodide 

PbI2 

•2Q   8OO 

Calcium  chloride.  .  .  . 
Calcium  bromide.  .  .  . 
Calcium  iodide  
Magnesium  chloride  . 

CaCl2 
CaBr2 
CaI2 
MgCl, 
MsO 

169,800 
140,900 

107,300 
217,300 

14^  QOO 

Lead  sulphate  
Lead  nitrate  
Stannous  chloride.  .  . 
Stannic  chloride.  .  .  . 
Auric  chloride 

PbSO4 

Pb(N03)2 
SnCl2 
SnCl4 
AuCl3 

2l6,20O 
105,500 
80,800 
127,300 

22  800 

Magnesium  hydroxide 
Aluminium  hydroxide 
Aluminium  chloride.  . 
Aluminium  bromide.  . 
Aluminium  iodide  .  .  . 
Ferrous  chloride  

Mg(OH)2 
A1(OH)3 
A1C13 
AlBr3 
Alia 
FeCl2 

217,300 
297,000 
151,000 

119,700 

70,400 
82,100 

Aurous  chloride.  .  .  . 
Aurous  bromide.  .  .  . 
Aurous  iodide  
Chloroplatinic  acid.  . 
Bromoplatinic  acid.  . 

AuCl 
AuBr 
Aul 
H2PtCl6 
H2PtBr6 

5,800 
—  IOO 

-5>5°o 
163,200 
88,400 

our  important  constant  of  96,540  coulombs,  we  should  be  able 
to  calculate  the  minimum  voltage  or  electromotive  force  necessary, 
and  consequently  the  energy  required,  to  break  up  any  chemical 
compound  by  electrolysis.  It  is  simply  converting  heat  energy 
into  electrical  energy.  We  must  of  course  know  the  relation  between 
the  calorie  and  the  joule,  and  should  commit  this  to  memory  as  a 
very  important  figure : 

i  joule  =0.00024  .Calorie 

i  joule  =0.24000  calorie 

Let  us  take  one  or  two  examples  and  work  them  out,  develop- 
ing a  practical  working  formula  for  future  use.  We  have  already 
learned  that  electrolytes  may  be  either  chemical  compounds  in 
solution  or  in  a  state  of  igneous  fusion.  As  we  have  dealt  with 
many  electrolytes  dissolved  in  water,  let  us  consider  an  electrolyte 


ENERGY  REQUIRED   IN   ELECTROLYSIS.  103 

in  a  state  of  fusion  by  heat.  Let  us  first  take  an  electrolyte  con- 
sisting of  monovalent  constituents,  and  consider  it  theoretically. 
Common  salt,  or  sodium  chloride,  will  serve  our  purpose,  with  its 
monovalent  sodium  linked  to  the  monovalent  chlorine.  In  cal- 
culating the  minimum  voltage  necessary  to  isolate  a  chemical  equiva- 
lent of  sodium  and  chlorine,  and  the  energy  necessary  to  effect  the 
electrolysis,  we  must  consider  the  gram-molecule  as  the  basis  of 
our  calculation,  which  in  the  case  of  sodium  chloride  is  58.5,  since 
sodium  has  an  atomic  weight  of  23,  and  chlorine  35.5.  There- 
fore 23+35.5=58.5.  58.5  grams  of  sodium  chloride  is  the 
gram-molecule  of  the  salt.  Glancing  at  the  table  of  "heats  of 
formation"  for  the  value  found  for  sodium  chloride,  we  see  it  to  be 
97,900  calories.  When  23  grams  of  sodium  combine  with  35.5 
grams  of  chlorine,  therefore,  to  form  58.5  grams  of  sodium  chloride, 
97,900  units  of  heat  are  set  free.  According  to  the  doctrine  of  the 
conservation  of  energy,  in  order  to  decompose  these  58.5  grams 
of  sodium  chloride,  an  amount  of  energy  equal  to  that  liberated 
at  the  time  of  formation  must  be  expended  upon  it  to  break  it 
up.  How  much  electrical  energy,  for  instance,  is  the  equivalent 
of  97,900  heat  units?  The  heat  unit  is  the  calorie,  and  we  have  just 
learned  that  0.24  Calorie  is  equal  to  the  joule.  97,900  calories 
divided  by  0.24  therefore  gives  us  the  joules  necessary  to  effect  the 
electrolysis. 

2^2??  =407,916  joules. 

We  have  learned  that  the  passage  of  96,540  coulombs  will  set 
free  the  chemical  equivalent  of  any  electrolyte,  and  we  see  from  the 
above  exposition  that  407,916  units  of  electrical  energy  are  neces- 
sary. In  order  that  the  passage  of  96,540  coulombs  should  repre- 
sent the  expenditure  of  407,916  joules,  they  must  be  supplied  at  an 
electrical  voltage  or  potential  of 


VOltS. 


96,540 


To  liberate  23  grams  of  sodium  and  35.5  grams  of  chlorine, 
therefore,  from  58.5  grams  of  sodium  chloride,  we  will  have  to 
expend  407,916  joules  of  electrical  energy,  and  it  will  be  necessary 


104  EXPERIMENTAL   ELECTROCHEMISTRY. 

to  have  a  voltage  of  at  least  4.22  volts  before  an  electrical  current 
can  be  made  to  pass  through.  Let  us  take  the  case  of  a  compound 
with  a  divalent  constituent,  for  example  magnesium  chloride  (MgCk) , 
from  which  to  theoretically  and  practically,  if  we  may  so  speak,  sep- 
arate the  chlorine  from  the  metal.  By  referring  again  to  our  table 
of  formation  heats,  we  find  for  the  gram-molecule  of  magnesium 
chloride  that  217,300  calories  are  liberated.  We  have  therefore: 

217,300 

=905,415  joules. 

0.2400 

Now  we  are  dealing  with  a  divalent  electrolyte,  and  according 
to  Faraday's  law  it  will  require  the  passage  of  96,540  +  96,540  cou- 
lombs to  separate  the  constituents.  This  gives  us: 

96,540 
96,540 

193,080  coulombs, 

which  must  be  divided  into  905,415  joules  in  order  to  obtain  the 
minimum  voltage 

2^ii       68  yolts. 
193,080 

It  is  evident  that  these  minimum  voltages  are  dependent  upon 
the  degree  of  accuracy  attained  in  the  determination  of  the  heat  of 
formation  of  the  compound  in  the  calorimeter,  which,  of  course, 
is  purely  a  thermochemical  operation.  It  must  be  stated,  however, 
as  a  matter  of  fact  in  an  actual  experiment  with  a  fused  electrolyte, 
that  the  calculated  voltages  are  a  little  high,  which  is  accounted 
for  by  the  high  temperatures  of  the  fused  compound.  At  the  tem- 
peratures of  igneous  fusion  the  heats  of  formation  have  a  lower 
value,  apart  from  the  fact  that  compounds  are  dissociated  in  the 
fused  state.  When  in  a  state  of  igneous  fusion,  therefore,  a  voltage 
of  something  less  than  the  calculated  pressure  will  drive  the  elec- 
trical current  through.  Let  us  perform  the  experiment  of  electri- 
cally separating  the  metal  magnesium  from  the  chloride,  and  measure 
the  electrical  energy  required.  Fig.  47  shows  the  equipment  which 
we  can  use  to  good  advantage,  both  as  a  laboratory  method  of  pro- 
ducing the  metal,  and  also  as  a  brilliant  lecture  experiment,  where 
a  large  mass  of  the  metal  is  produced  and  hammered  out  and  ignited 


ENERGY  REQUIRED   IN   ELECTROLYSIS.  105 

to  produce  the  dazzling  magnesium  light.     At  the  left  in  this  illus- 
tration we  have  the  motor-generator,  with  the  controlling  rheostats 


FIG.  47.  —  Experimental  Equipment  for  Lecture-room  or  Laboratory  for  Electrically 
Isolating  Metallic  Magnesium  from  its  Chloride.  Motor-generator  with  rheo- 
stats at  left.  Copper  voltameter  in  center,  and  small  fusion-furnace  at  right. 

for  supplying  a  heavy  current  at  low  electrical  pressure.  The 
furnace  is  of  the  small  gas-fusion  type,  which  contains  an  iron  pot  for 
the  electrolyte,  and  which,  as  can  be  seen,  is  made  the  cathode. 
The  anode  consists  of  a  large  rod  of  carbon  passing  through  a  tight- 
fitting  cover.  A  large  copper  voltameter  is  depicted  in  the  center 
for  determining  the  number  of  coulombs  passed,  and  electrical  in- 
struments are  connected  to  the  leads  to  indicate  the  voltage  and 
current  strength.  For  our  experimental  purposes  an  artificial 
carnalite  will  best  serve  our  purpose  for  the  electrolyte.  The  com- 
position of  this  mineral  may  be  set  down  as  follows: 


KMgCl3,  6H20  =  KCl  +  MgCl2  +  6H20  =MgCl2  34-2, 
KC1  26.9,  H2O  38.9  =  100. 

For  our  purpose  we  can  prepare  an  easily-fused  artificial  carnalite 
by  evaporating  to  dryness  on  a  water-bath  a  solution  of 

400  grams  of  crystallized  magnesium  chloride, 
150  grams  of  potassium  chloride, 
60  grams  of  ammonium  chloride. 


106  EXPERIMENTAL   ELECTROCHEMISTRY. 

This  residue  may  be  placed  in  a  large  salt-mouthed  bottle  for 
use  as  required.  For  an  experimental  run  the  iron  vessel  in  which 
the  electrolysis  is  to  be  carried  on  is  carefully  cleaned  on  the  inside 
by  means  of  sandpaper,  to  remove  any  rust  and  to  produce  a  bright 
metallic  surface  from  which  the  magnesium  is  easily  separated. 
This  iron  pot  is  so  connected  as  to  form  the  cathode,  and  is  placed 
in  the  furnace  and  the  gas  lighted.  A  small  piece  of  charcoal  is 
put  in  the  pot  to  prevent  oxidation  as  it  heats  up.  When  a  faint 
red  glow  is  seen  in  the  bottom  of  the  iron  pot,  the  artificial  carnalite 
is  slowly  added,  allowing  each  addition  to  fuse  and  run  before  the 
next  portion  is  added.  The  pot  may  in  this  way  be  nearly  filled, 
when  the  carbon  anode  is  placed  in  position  through  the  top.  Now, 
as  magnesium  is  a  very  light  metal  and  often  rises  to  the  top  of 
the  electrolyte  after  being  isolated,  when  it  takes  fire  and  is  de- 
stroyed, it  is  necessary  to  protect  it.  For  this  purpose  a  tight-fitting 
top  is  the  best  precaution,  fitted  with  asbestos  plugs  through  which 
hard-glass  tubes  pass  as  indicated  in  the  drawing.  By  means  of 
these  tubes  a  gas  can  be  passed  which  displaces  the  oxygen  present, 
and  prevents  the  combustion  of  the  magnesium.  The  present 
writer  has  connected  these  glass  intake-tubes  direct  to  the  city  light- 
ing gas-supply  with  much  success,  allowing  the  coal-gas  and  chlorine 
to  be  led  away  to  a  hood.  In  this  way  we  have  the  magnesium 
completely  protected  from  possibilities  of  combustion,  since  coal-gas 
being  a  mixture  of  hydrocarbons,  etc.,  does  not  support  combus- 
tion. For  an  experiment,  therefore,  the  top  is  placed  in  position 
after  the  chlorides  have  fused  to  a  clear,  transparent  liquid,  and 
coal-gas  is  passed  through  the  space  over  the  electrolyte  when 
the  electrical  current  is  started.  The  magnesium  separates 
smoothly,  and  may  be  ladled  out  and  cast  into  molds,  care  being 
taken  to  allow  the  electrolyte  to  cool  down  considerably  before 
exposing  it  to  the  air,  as  it  is  very  likely  at  high  temperature  to  take 
fire  and  burn  with  its  characteristic  dazzling  light.  Of  course,  for 
a  full  efficiency  determination  of  such  a  process  an  accurate  gas- 
meter,  with  the  necessary  observations  for  gas  temperature  and 
atmospheric  pressure,  should  go  in  with  the  burner.  For  a  com- 
plete physical  and  electrical  study  of  the  isolation  of  magnesium, 
the  heat  value  of  the  fuel-gas  per  cubic  foot  should  be  determined 
by  means  of  a  suitable  calorimeter.  There  are  several  calorimeters 


ENERGY   REQUIRED   IN   ELECTROLYSIS.  107 

especially  designed  for  determining  the  heating  value  of  gaseous 
fuels.  With  our  copper  voltameter  and  reliable  voltmeter  we  will 
be  in  possession  of  the  essential  data  for  interesting  figures  taken 
in  connection  with  the  weight  of  metal  produced.  This  experi- 
ment is  capable  of  going  still  further,  using  the  liberated  chlorine, 
for  example,  to  prepare  chloride  of  lime.  For  this  purpose  we 
should  prepare  a  lead  box  with  lead  shelves,  upon  which  we  can 
lay  out  a  quantity  of  moist  slaked  lime.  The  temperature  is  not 
allowed  to  rise  above  25°,  which  is  controlled  by  diluting  the  chlorine 
passing  into  the  chamber  with  air.  The  constitution  of  chloride 
of  lime  is  not  known  with  certainty,  but  the  action  between  the 
chlorine  and  the  moist  slaked  lime  may  be  represented  as  follows: 


Ca(OH)2  +  Cl2  =  CaCl(OCl)  +H2O. 

Thus  a  very  pretty  by-product  may  be  obtained  at  the  time  of  iso- 
lating the  metallic  magnesium. 

Let  us  take  a  case  of  a  non-igneous  electrolyte,  and  calculate 
the  minimum  voltage  required.  We  are  almost  unlimited  in  a 
selection  of  these  cases,  and  for  this  reason  a  novel  case  of  electrol- 
ysis as  conducted  by  the  author,  to  show  that  sulphuric  acid  con- 
sists of  hydrogen,  oxygen,  and  sulphur,  may  be  of  special  interest. 
This  is  an  interesting  lecture  experiment  for  both  beginners  in  general 
chemistry  and  for  those  advanced  in  physical  chemistry  as  well. 
We  all  know  that  dilute  sulphuric  acid  electrolyzes  into  hydrogen 
and  oxygen  gases,  and  that  these  gases  are  liberated  in  the  propor- 
tion of  two  volumes  of  hydrogen  to  one  volume  of  oxygen.  The 
writer  has  conducted  numerous  experiments  with  concentrated 
sulphuric  acid,  and  by  the  proper  adjustment  of  concentration, 
current  density,  temperature,  etc.,  has  been  able  to  electrolyze  the 
acid  into  hydrogen,  oxygen,  ozone,  and  free  sulphur,  and  at  ele- 
vated temperatures  into  hydrogen,  oxygen,  sulphur  trioxide,  and 
ozone.  Fig.  48  illustrates  the  apparatus  for  conducting  such  elec- 
trolysis. At  the  left  we  have  a  bell  jar  covering  the  beaker  con- 
taining the  strongest  chemically-pure  sulphuric  acid  over  a  dehy- 
drating agent,  such  as  calcium  chloride.  A  thermometer  is  fitted 
through  the  stopper  as  shown,  and  the  electrical  equipment  includes 
electrical  instruments  for  observing  the  energy  conditions.  The 


io8 


EXPERIMENTAL   ELECTROCHEMISTRY. 


motor-generator  is  shown  at  the  extreme  right  with  the  controlling 
rheostats,  although  the  lamp-bank  serves  equally  well,  if  not  better, 


FlG.  48.  —  Apparatus  for  the  Electrolysis  of  Concentrated  Sulphuric  Acid  to  obtain  as 
Electrode  Products  Hydrogen,  Oxygen,  Ozone,  and  Free  Sulphur  which  may  be 
Exhibited  upon  the  Anode  and  be  Burned.  Therefore,  sulphuric  acid  may  be 
directly  broken  down  into  its  elements. 

for  this  particular  experiment.  Upon  passing  a  sufficiently  heavy 
current  through  the  concentrated  acid  we  get  free  sulphur,  together 
with  ozone,  oxygen,  and  hydrogen,  as  indicated  in  the  accom- 
panying equation  : 


The  sulphur  deposits  upon  the  anode  and  may  be  burned  with  its 
characteristic  blue  flame  before  a  class  to  show  its  presence.  The 
ozone  may  be  detected  by  moistening  a  piece  of  filter-paper  in  starch 
and  potassium  iodide  preparation,  and  holding  it  near  the  anode 
during  electrolysis.  The  hydrogen  may  be  collected  and  burned. 
The  minimum  voltage  for  conducting  such  an  experiment  may 
be  calculated  by  means  of  our  formula  to  a  fair  degree  of  precision. 
As  we  are  now  in  a  position  to  follow  theoretically  as  well  as  practi- 
cally an  electrochemical  process,  the  writer  introduces  what  he 
believes  to  be  the  "mechanism"  of  this  particular  electrolysis.  In 
all  our  practical  work  we  must  endeavor  to  account  theoretically 
for  the  phenomena  involved  in  practice,  for  it  is  the  man  with  the 
insight  into  both  theory  and  practice  who  makes  the  best  invest- 


ENERGY  REQUIRED  IN   ELECTROLYSIS. 


109 


tigator.  Having  calculated  the  minimum  voltage  and  energy  re- 
quired, and  conducted  an  actual  electrolysis,  we  should  certainly 
endeavor  to  express  that  which  takes  place  in  concise  and  scientific 
manner.  In  the  almost  classic  case  of  sulphuric  acid  and  water, 
the  acid  is  believed  to  dissociate  into  the  ions 


H2  and   SC>4. 

The  SO  4,  instead  of  being  set  free,  decomposes  the  water  present, 
as  indicated  as  follows,  taking  up  the  two  atoms  of  hydrogen  present, 
to  form  sulphuric  acid  and  liberating  oxygen.  As  the  result  of  certain 
research  work  upon  the  concentrated  acid,  it  is  believed  to  dissociate 

4- 

into  the  ions  H  and  HSO4. 


Cathode  , 


SO- 


jbwde 


Now,   according  to   recent   research  upon  the   conductivity   of 

pure  water,  water  itself  is  found  to  be  slightly  dissociated  (about 

+ 
one  molecule  in  a  million  being  broken  down  thus:  H  OH)   and 

taking  this  fact  into  account,  we  may  have  upon  this  basis  the  libera- 
tion of  two  volumes  of  hydrogen  and  one  volume  of  oxygen  equally 
well  accounted  for  in  diagram. 


E50 


Now  let  us  write  the  structural  formula  of  sulphuric  acid,  and 
endeavor  to  represent  the  " mechanism"  of  electrolysis  when  we 
obtain  hydrogen,  oxygen,  ozone,  and  free  sulphur. 

H-O-Q=O 
H-0-    =0. 


no 


EXPERIMENTAL   ELECTROCHEMISTRY. 


Here  we  have  the  sulphur  acting  with  the  valence  of  six,  and  a 
scheme  indicating  the  linking  of  the  acid.  How  can  it  electrolyze 
and  give  such  products?  The  following  diagram  shows  the  prob- 
able manner  taking  dissociated  water  into  account: 


\R\-0-     «!d| 


Here  we  also  have  the  formation  of  a  molecule  of  water  within  the 
electrolyte.  If,  however,  the  temperature  is  allowed  to  rise  above 
105°  C.  we  obtain  hydrogen,  oxygen,  and  sulphur  trioxide,  with 
the  formation  of  a  molecule  of  water  within  the  electrolyte  as  follows : 


-  o  -  ,- 


M 

{  o  ' 


-._-. 


So  much  for  this  side  of  electrolysis  and  the  part  played  by 
minimum  voltage,  or  electrode  tension  as  a  factor  in  experimental 
as  well  as  in  commercial  work. 


ELECTROLYTIC    SEPARATION   OF   METALS. 

Under  the  present  heading  we  will  take  up  the  art  of  electro- 
analysis,  and  separate  one  metal  from  another,  when  both  exist 
in  the  same  solution,  through  the  proper  adjustment  of  electrode 
tension.  Fig.  49  shows  a  plan  for  accomplishing  this.  Here  we 
have  a  platinum  dish  resting  upon  a  platinum  plate,  connected  with 
the  negative  wire  of  a  storage-battery  and  variable  rheostat.  A 
disk  of  platinum  welded  to  a  platinum  wire  is  suspended  in  the 
dish  to  serve  as  anode,  and  is  connected  in  turn  with  the  battery. 
A  delicate  ammeter  and  voltmeter  complete  the  equipment,  and 
are  joined  up  as  shown.  Only  instruments  of  delicacy  and  pre- 
cision are  applicable  for  this  class  of  work,  and  a  rheostat  capable 


ELECTROLYTIC  SEPARATION  OF  METALS 


ill 


of  fine  graduations  is  absolutely  essential.    The  cells  of  the  battery 
must  be  so  arranged  that  one  or  more  may  be  joined  in  series  in  a 


FIG.  49. — Method  of  Separating  Metals  by  Electrodeposition  through  Adjustment 

of  Electrode  Tension. 

convenient  manner.  Having  set  up  the  apparatus,  we  are  in  a 
position  to  undertake  some  experimental  work.  Fig.  50  illustrates 
a  practical  working  equipment  for  separating  one  metal  from  an- 
other on  the  basis  of  electrode  tension.  A  platinum  dish  and  plati- 
num strip  acting  as  the  cathode  and  anode  respectively  are  shown 
in  the  center.  Readers  of  electrochemical  literature  will  in  this 
connection  come  across  the  terms  "polarization"  and  " polariza- 
tion current,"  etc.,  which  refer  to  the  back  electromotive  force 
or  tension  necessary  in  order  to  force  a  current  through  an  electro- 
lyte. Therefore,  polarization  may  be  under  tood  to  refer  to  the 
minimum  voltage  necessary  to  effect  an  electrolysis.  Le  Blanc 
made  many  c  reful  researches  upon  the  electrode  tensions  neces- 
sary to  decompose  various  salts,  acids,  and  bases  when  in  solution, 
and  it  may  be  easily  seen  that  we  may  separate  one  constituent 
from  another  in  an  electrolyte  by  carefully  adjusting  the  electrode 
tension  to  fall  between  the  two  different  values  for  the  different 


112 


EXPERIMENTAL   ELECTROCHEMISTRY. 


electrolytes.     Le  Blanc  found  the  following  values  for  normal  solu- 
tions : 

Volts.  Volts. 

ZnS04 2.35      Cd(N03)2. 

ZnBr2 i .  80 

NiSO4 2.09 

NiCl2 

Pb(N03)2 

AgN03 

HNO, 

NaOH 

NH4OH 

This  is  of  course  only  a  partial  list,  but  will  be  sufficient  to  serve 
as  a  useful  guide  in  the  laboratory.    Any  attempt  to  outline  methods 


1.  80 

CdSO4  

2  .OO 

CdCl2  

88 

•  ">2 

CoCl2  

T8 

•  7o 

H2SO4  

67 

60 

HC1  

.69 

KOH  

67 

.74. 

HBr.  .                                               .    < 

)  .  Od. 

FIG.  50. — The  Separation  of  Metals  by  Adjustment  of  Electrode  Tension.  Rheo- 
stats, storage-batteries,  and  electrical  instruments  are  shown  here  in  practical 
operation  in  the  laboratory. 

of  electro-analysis  would  be  incomplete  at  this  time  without  intro- 
ducing the  attractive  and  useful  device  known  as  the  rotating  anode. 
Suppose,  for  example,  it  is  wished  to  determine  copper  in  the  electro- 
lytic way,  that  is  by  deposition  upon  a  platinum  dish.  According 
to  the  old  scheme,  we  had  the  dish  and  a  stationary  anode.  With 
this  arrangement  it  was  necessary  to  work  with  a  feeble  current,  or 
else  the  deposit  of  copper  would  come  down  dark  and  non-adherent. 
For  this  reason  it  took  many  hours,  very  often,  to  produce  com- 
plete precipitation.  With  the  rotating  anode,  the  current  strength 
can  be  enormoulsy  increased,  and  yet  obtain  a  beautiful  pink  ad- 
herent deposit  of  copper  in  a  correspondingly  shorter  time.  Here 


ELECTROLYTIC   SEPARATION   OF  METALS.  113 

we  have  an  electric  motor  properly  wound  to  run  on  a  storage-battery 
circuit,  or  else  especially  wound  to  run  on  the  electric-lighting  circuit 
with  lamps  in  parallel.  Do  not  try  to  use  a  very  small  motor.  Pro- 
cure one  several  sizes  larger  than  is  really  necessary  to  revolve  the 
anode,  for  it  can  be  much  more  easily  controlled  through  the  agency 
of  our  lamp-bank,  or  a  special  short  bank  as  illustrated  at  the  extreme 
right  in  Fig.  51.  Here  the  addition  of  one  lamp  will  give  the  motor 


FIG.  51. — Easily -constructed  Rotating  Anode  for  Rapidly  Conducting  Electro-analy- 
sis. With  this  equipment  an  electro-analysis  may  be  completed  in  a  few  min- 
utes, which  would  require  several  hours  to  accomplish  in  the  old  way. 

a  certain  speed,  which  may  be  increased  by  the  addition  of  others. 
From  thirty  to  one  hundred  and  twenty  revolutions  per  minute 
have  been  found  to  be  excellent  speeds,  although  higher  speeds 
may  be  used  with  advantage  so  long  as  there  is  no  danger  of  losing 
electrolyte  by  its  spinning  out  of  the  dish.  A  large  disk  just  above 
the  platinum  dish  should  be  included  in  the  equipment,  to  prevent 
anything  falling  into  the  dish  from  the  commutator  and  contact 
brushes  above.  The  rest  of  the  make-up  is  so  simple  that  the 
illustration  should  serve  to  make  it  clear.  A  few  words  concerning 
the  principle  upon  which  the  rotating  anode  accomplishes  its  rapid 
precipitation  may  be  given  here.  The  main  thing  accomplished 
by  the  rotating  anode  is  to  keep  the  solution  homogeneous  in  character. 
Let  us  take  the  case  of  a  solution  of  copper  sulphate.  If  a  com- 
paratively feeble  current  of  electricity  be  passed  through  an  electro- 


114  EXPERIMENTAL  ELECTROCHEMISTRY. 

lyte  consisting  of  copper  sulphate  for  a  long  time,  there  are  concen- 
tration changes  set  up.  If  we  use  copper  electrodes  the  anode  loses 
in  weight  just  as  much  as  the  cathode  gains,  and  there  is  at  all  times 
in  the  solution  the  same  amount  of  copper,  or  to  put  it  in  other 
words,  there  is  always  the  same  number  of  copper  ions  in  solution. 
Now,  even  with  the  use  of  copper  electrodes  and  a  constant  number 
of  copper  ions  present  in  the  solution,  concentration  changes  will 
be  set  up  if  the  current  is  allowed  to  flow  for  any  considerable  length 
of  time.  In  such  an  experiment  it  is  found  with  copper  sulphate, 
for  example,  that  we  get  an  increase  of  concentration  at  the  anode 
and  a  decrease  of  concentration  at  the  cathode.  Fig.  52  represents 
the  condition  of  affairs  in  a  vertical  glass  tube  containing  copper 
electrodes  and  an  electrolyte  of  copper  sulphate.  The  shaded 
portion  represents  the  concentration  of  the  solution  about  the  anode. 
Now,  if  this  took  place,  as  it  does  with  a  platinum  dish  and  station- 
ary anode,  the  copper  ions  become  so  few,  or  in  other  words  the 
electrolyte  becomes  so  poor  in  copper  about  the  cathode  dish,  that 
we  are  held  down  to  the  use  of  a  feeble  current  or  there  will  be 
trouble  in  getting  the  adherent,  pink  deposit,  so  necessary  for  all 
accurate  determinations  of  copper  by  electro-deposition.  How  can 
these  concentration  changes  be  overcome?  The  rotating  anode 
accomplishes  this  perfectly,  and  enables  us  to  keep  a  constant  supply 
of  copper  ions  about  the  cathode  dish,  and  allows  consequently  of 
a  heavy  current  being  employed.  How  can  we  explain  the  con- 
centration changes  ?  Fig.  53  shows  by  diagram  how  such  accumula- 
tion of  copper  ions  about  the  anode  is  accounted  for  according  to 
Hittorf.  The  changes  in  concentration  calculated  from  one  of 
Hittorfs  researches  are  shown  in  this  diagram.  Here  the  white 
circles  represent  the  anions  and  the  black  circles  the  cathions,  and 
the  dotted  horizontal  line  indicates  merely  the  middle  of  the  solu- 
tion in  the  vertical  containing  vessel.  The  electrolyte  is  perfectly 
homogeneous  before  the  electric  current  is  passed,  as  is  seen  by 
an  equal  number  of  anions  and  cathions  respectively  on  each  side 
of  the  line.  In  the  figure  we  have  nine  upon  each  side.  Now 
allow  the  current  to  pass  for  a  given  time.  We  know  that  different 
ions  have  different  velocities,  and  consequently  the  Cu  ions  will 
move  in  one  direction  at  a  different  rate  from  the  864  ions  moving 
in  the  other  direction.  It  is  very  often  confusing  to  the  student 


ELECTROLYTIC  SEPARATION   OF  METALS. 


to  understand  how  we  can  have  such  concentration  changes  due 
to  different  velocities  of  the  ions  when  we  have  the  same  equivalents 
of  ions  liberated  at  anode  and  cathode  respectively.  No  cathion 
can  separate  at  the  cathode  until  an  anion  separates  at  the  anode, 
and  for  each  and  every  ion  which  is  liberated  at  one  electrode  there 
must  be  a  corresponding  ion  liberated  at  the  other.  There  may, 


I      n 


FIG.  52.  FIG.  53.  FIG.  54. 

FIG.  52. — Experiment  with  Copper-sulphate  Solution  to  show  Concentration  Changes, 
wrought  by  a  Feeble  Current  Flowing  for  a  Long  Time.  The  electrodes  are  of 
copper. 

FIG.  53. — Diagram  Representing  Hittorf's  "Transport  Numbers."  From  Hittorf's, 
researches  the  relative  velocities  of  ions  are  determined  experimentally,  by  con- 
centration changes. 

FIG.  54. — Approved  Apparatus  of  Mather  and  Jones  for  Experimentally  determining 
the  Relative  Velocities  of  Ions  Based  upon  Concentration  Changes. 

of  course,  be  the  case  where  we  have  one  divalent  ion  separating  at 
one  pole  and  consequently  two  univalent  ions  separating  at  the 
other.  Faraday's  law  teaches  us  this.  As  a  result  of  the  different 
velocities,  while  we  have  an  anion  liberated  for  every  cathion,  we 
may  have  a  banking  up  of  the  swifter  kind  of  ions,  and  so  to  speak, 
ready  to  discharge.  This  is  illustrated  in  the  little  diagram  at  the 
right,  where  we  have  thirteen  anions  across  the  dotted  line  and 


n6  EXPERIMENTAL   ELECTROCHEMISTRY 

only  eleven  cathions  across  the  dividing  line  in  the  opposite  direc- 
tion. Such  concentrations  may  be  practically  shown  by  experiment 
with  a  piece  of  apparatus  as  illustrated  in  Fig.  54,  as  devised  by 
Mather,  working  with  Jones.  Here  a  copper-sulphate  solution, 
for  example,  may  be  electrolyzed,  and  the  solution  drawn  off  from 
the  two  tubes  respectively  and  analyzed  for  concentration.  Know- 
ing the  original  concentration  of  the  homogeneous  electrolyte,  the 
number  of  coulombs  passed,  and  the  respective  concentrations  of 
the  respective  anode  and  cathode  tubes,  we  have  all  the  data  for 
determining  the  relative  velocities  of  the  two  ions.  This  is  a  very 
practical  piece  of  apparatus,  and  with  it  very  interesting  concen- 
tration changes  may  be  studied. 


CHAPTER  VIII. 

IMPORTANT  CONDITIONS  TO  BE  NOTED  IN  ELECTROCHEM- 
ICAL OPERATIONS.  CAUSTIC  SODA  AND  CHLORINE  FROM 
SALT.  ELECTROLYTIC  PRODUCTION  OF  WHITE  LEAD. 
ELECTROLYTIC  PRODUCTION  OF  CADMIUM  YELLOW. 
ELECTROLYTIC  PRODUCTION  OF  MERCURY  VERMILION. 
ELECTROLYTIC  PRODUCTION  OF  SCHEELE'S  GREEN. 
ELECTROLYTIC  PRODUCTION  OF  BERLIN  BLUE. 

VARIOUS  controlling  conditions  must  be  observed  in  all  electro- 
chemical operations,  and  be  recorded  in  connection  with  every  piece 
of  experimental  work.  There  are  many  governing  adjustments  or 
conditions  in  electrolysis,  without  a  working  knowledge  of  which  the 
student  will  be  unable  to  meet  with  any  notable  success  in  carrying 
out  a  determination,  or  be  able  to  obtain  the  same  result  twice  in 
any  undertaking.  One  of  the  most  important  factors  in  all  electro- 
chemical work  is  that  of  "  current  density,"  and  because  of  its  great 
moment  and  importance  it  will  be  dealt  with  at  the  opening  of  this 
chapter.  Current  density  depends  upon  the  ratio  of  electrode  area 
to  the  current  flow  in  an  electrolytic  cell.  We  may  have  high-current 
density  at  both  electrodes,  or  low-current  density  at  both  electrodes, 
01  else  high-current  density  at  one  of  them  and  low-current  density 
at  the  other.  Fig.  55  has  been  designed  to  make  this  clear.  At  the 
left  in  this  diagram  the  anode  is  simply  a  thin  platinum  wire  affording 
but  small  surface  from  which  the  electric  current  can  leave  to  enter 
the  electrolyte,  whereas  the  cathode  is  a  platinum  sheet  affording 
a  large  surface  for  the  same  current  to  b£  conducted  from.  At  the 
right  in  the  same  diagram  the  conditions  of  current  density  are 
just  reversed.  Now  the  point  of  interest  lies  in  the  fact  that  adjust- 
ments of  current  density  have  an  important  effect  upon  almost  all 
electrochemical  operations,  determining  the  character  of  the  electrode 
products,  as  well  as  the  chemical  change  which  may  take  place 

117 


n8 


EXPERIMENTAL  ELECTROCHEMISTRY. 


throughout  the  entire  electrolyte.  Oxidation  and  reduction  are  two 
of  the  most  important  chemical  phenomena,  and  yet  the  oxidation  or 
reduction  of  an  electrolyte  may  be  brought  about  by  the  same  electric 
current,  the  only  difference  in  its  application  being  that  of  current 
density.  The  following  rule  should  be  learned  by  all  electrochemical 
students: 

Oxidation  is  effected  by  using  concentrated  electrolytes  and  by 
a  low-current  density  at  the  anode,  as  depicted  in  the  right-hand 
cell  in  the  illustration.  Reduction  is  effected  by  using  concentrated 

-  -F- 


FIG.  55.  FIG.  56. 

FIG.  55. — Diagram  to  Show  Two  Different  Conditions  of  Current  Density.  At  the 
left  there  exists  high-current  density  at  the  anode  and  low-current  density  at  the 
cathode.  In  the  cell  depicted  at  the  right  we  have  low-current  density  at  the 
anode  and  high-current  density  at  the  cathode. 

FIG.  56. — Four  Cells  in  Series  receiving  a  Common  Current,  but  because  of  Dissimilar 
Current  Density  Adjustments,  Electrolytes  in  the  Several  Cells  will  Yield  Differ- 
ent Decomposition  Products.  The  electrolysis  in  the  two  cells  at  the  left  will 
be  the  same,  but  will  differ  from  the  products  in  the  two  cells  at  the  right. 

electrolytes  and  a  low-current  density  at  the  cathode,  as  depicted 
in  the  left-hand  cell  in  the  illustration. 

It  will,  therefore,  be  fully  appreciated  how  very  important  it  is  to 
note  and  take  fully  into  account  the  conditions  of  current  density  in 
any  piece  of  experimental  work.  Fig.  56  illustrates  four  cells  in 
series,  the  whole  system,  therefore,  receiving  a  common  electric 
current.  The  conditions  of  current  density,  however,  are  not  the 
same,  and  we  will  obtain  different  results  in  the  two  cells  at  the  right 
from  those  in  the  two  cells  at  the  left.  To  test  this  we  can  perform 
the  following  simple  experiment,  using  a  solution  of  oxalic  acid  for 
the  electrolytes,  to  which  has  been  added  a  quantity  of  sulphuric  acid. 
Take  60  grams  of  oxalic  acid  to  the  liter  of  water,  and  add  50 
grams  of  sulphuric  acid,  and  place  an  equal  portion  of  this  solution 
in  each  of  the  four  cells.  A  current  of  about  half  an  ampere  is 
allowed  to  flow  for  an  hour,  when  the  oxalic  solution  in  each  cell 
is  determined  by  means  of  permanganate  of  potassium.  Oxidation 


ELECTROCHEMICAL   OPERATIONS. 


119 


will  be  found  to  have  taken  place  in  the  two  right-hand  cells  if  the 
current  adjustment  is  as  shown  in  the  diagram,  and  is  equal  for 
each  cell.  At  the  left  there  will  be  no  notable  increase,  although 
we  do  not  get  a  correspondingly  great  reduction.  It  should  be  stated 
that  these  current  density  conditions  exert  a  strong  tendency  to 
oxidize  and  reduce  respectively,  but  of  course  all  electrolytes  are 
not  oxidizable  or  reducible  any  more  than  many  compounds  are 
which  go  to  make  them  up.  We  know  that  oxidation  is  usually 
accompanied  by  liberation  of  heat,  and  it  is  therefore  of  great  moment 
to  know  both  the  anode  and  cathode  temperatures  in  an  electro- 
chemical research.  Fig.  57  illustrates  the  plan  of  the  author  for 


FIG.  57. — Author's  Arrangement  of  Two  Sensitive  Beckmann  Thermometers  to 
Study  Anode  and  Cathode  Temperatures,  when  Making  a  Research  upon  an 
Electrolyte. 

investigating  such  differential  heat  liberation.  What  are  some  of 
the  other  important  conditions  to  be  observed?  They  are  many 
and  vital,  and  it  is  deemed  that  a  concise  tabulation  of  them,  as 
arranged  by  the  author  for  use  in  the  laboratory,  will  be  perhaps  a 


120  EXPERIMENTAL   ELECTROCHEMISTRY. 

good  way  of  presenting  them.  In  making  any  kind  of  a  research 
upon  a  solution  when  subjected  to  the  action  of  an  electric  current, 
the  conditions  tabulated  here  should  be  taken  account  of.  If  a  piece 
of  experimental  work  is  to  be  undertaken,  a  neatly-kept  notebook 
should  of  course  be  opened,  and  a  careful  record  kept  of  each  thing 
observed,  together  with  all  the  existing  conditions.  It  will  be  neces- 
sary to  make  a  number  of  repeated  special  runs  to  secure  all  the  data 
as  advised  in  the  accompanying  table,  as  there  are  too  many  conditions 
to  be  usefully  observed  and  recorded  during  any  one  run.  For 
example,  a  special  run  may  have  to  be  made  for  differential  tem- 
peratures, another  for  specific  gravity  determinations,  etc.  In 
several  runs  the  following  table  may  be  compiled  for  Teference. 
This  particular  table  was  the  result  of  the  author's  work  upon 
sulphuric  acid. 

Duration  of  run One  hour 

Compound  electrolyzed H2SO.. 

Character  of  solution No  solution 

Sp.  gr.  before  electrolysis i  .84664 

Sp.  gr.  after  electrolysis i  .84001 

Quantity  of  compound  taken 100  c.c. 

Character  of  apparatus See  illustration 

Dimensions  of  cell 7X8  cm. 

Source  of  electricity Motor-generator 

Temperature  of  electrolyte 21 . 5°  C. 

Temperature  at  anode 21 . 5°  C. 

Temperature  at  cathode 21 . 5°  C. 

Amperes  flowing 4 . 250 

Volts  indicated 16.00 

Area  of  anode  immersed 4  sq.  cm. 

Area  of  cathode  immersed 4  sq.  cm. 

Current  density  at  anode -^ioo=  106.2 

Current  density  at  cathode C'loo^  106.2 

Distance  between 3  cm. 

Phenomenon  at  anode SO3  and  O 

Phenomenon  at  cathode. Hydrogen 

Phenomenon  between Floating  S  in  3  mins. 

Secondary  action  at  anode None  at  once 

Secondary  action  at  cathode None  at  once 

Secondary  action  between None 

Later  phenomenon  at  anode SO3  at  103.5°  C« 

Later  phenomenon  at  cathode None 

Later  phenomenon  between Increased  S 

Material  of  anode Platinum 

Material  of  cathode Platinum 

Material  of  containing  cell Glass 

Special  peculiarities 


ELECTROCHEMICAL   OPERATIONS.  121 

Many  operations,  of  course,  will  not  require  the  setting  down  of 
so  many  data,  but  for  all  research  purposes  the  student  will  do 
well  to  tabulate  his  facts  as  completely  as  possible.  We  are  now 
in  a  position  to  produce  electrolytic  preparations,  and  a  few  interest- 
ing examples  for  laboratory  practice  are  given  here. 


CAUSTIC   SODA   AND   CHLORINE   FROM   COMMON   SALT. 

This  is  one  of  the  first  laboratory  exercises  the  student  in  experi- 
mental electrochemistry  should  take  up  in  the  way  of  preparations. 
The  experiment  is  a  very  practical  and  easily  carried  out  introduction 
to  electrochemical  manufacture.  The  apparatus  as  illustrated  in 
the  photograph  in  Fig.  58  is  easily  and  quickly  put  together  in  any 
laboratory,  and  serves  a  most  useful  purpose  in  many  cases  of  elec- 
trolysis where  the  anode  gas  is  to  be  collected.  The  apparatus 
simply  consists  of  a  large  beaker  glass  containing  a  good-sized  porous 
pot,  about  which  a  cylinder  of  nickel- wire  gauze  is  placed  to  form 
the  cathode  of  the  cell.  A  cylindrical  lamp-chimney  is  next  procured, 
and  fitted  with  a  heavy  rubber  stopper,  through  which  passes  a  rod 
of  carbon  to  serve  as  the  anode.  There  is  a  second  hole  in  this 
stopper,  to  receive  a  small  glass  tube,  through  which  the  chlorine 
escapes  from  the  glass  lamp-chimney  chamber.  The  rubber  stopper 
should  be  given  several  coats  of  paraffin  wax  inside  and  out  with  a 
good  brush  dipped  into  a  melted  mass.  The  electrolyte  consists 
simply  of  a  saturated  solution  of  common  salt  in  water,  and  our 
lamp-bank  with  two  or  three  lamps  in  parallel  in  connection  with 
an  electric-lighting  system  completes  the  equipment.  Chlorine  gas 
escapes  copiously  from  the  anode  chamber,  and  a  corresponding 
quantity  of  sodium  hydroxide  is  formed  in  the  cathode  chamber. 
Hydrogen  of  course  escapes  from  the  nickel-wire  gauze  when  the 
salt  breaks  up  in  accordance  with  the  following  equation: 

2NaCl  +  2H2O  =  2NaOH  +  H2  +  C12. 

The  chlorine  should  be  led  into  a  lead-lined  box  containing  lead 
shelves  holding  moist  calcium  oxide,  as  outlined  in  the  electrolysis 
of  magnesium  chloride,  for  the  simultaneous  production  of  chloride 
of  lime,  or  the  chlorine  may  be  led  into  water  to  saturate  it  for 


122 


EXPERIMENTAL  ELECTROCHEMISTRY. 


bleaching   purposes.       The  liquid    from    the  cathode   chamber  is 
poured   off  after  the  run,  and  evaporated  to  dryness  in  a  porcelain 

dish  to  obtain  the  solid  caustic  soda. 
This  experiment  can  and  should  be  run 
quantitatively  by  including  a  copper 
voltameter  in  series  with  it,  and  noting 
the  fall  in  voltage  between  the  electrodes, 
in  order  that  we  may  state  the  number  of 
joules  absorbed  per  gram  of  sodium 
hydroxide  produced,  and  per  gram  of 
bleaching-powder,  etc.  The  porous-pot 
partition  in  this  apparatus  plays  a  most 
important  part,  as  it  keeps  the  chlorine 
set  free  from  acting  upon  the  caustic 
soda  formed  to  produce  another  com- 
pound, namely,  sodium  hypochlorite.  As 
the  use  of  porous  pots  is  of  great  impor- 

FIG.  58.— Large  Beaker  Ar-  .  11- 

ranged  with  Porous  Pot  and  tance  m  a  g^at  many  electrolytic  opera- 
Glass  Anode  Chamber  for  Pro-  tions  as  well  as  in  research  and  investi- 
dudng  Caustic  Soda  and  Chlo-  gations,  a  group  of  the  various  desirable 

shapes  and  sizes  has  been  photographed, 

which  constitutes  Fig.  59.      A  good  supply  of  these  should  be  at 

hand  in  every  electrochemical  laboratory. 


ELECTROLYTIC    PRODUCTION    OF    WHITE    LEAD   FROM    METALLIC   LEAD 

ELECTRODES. 

A  very  beautiful  electrolytic  preparation  is  that  of  white  lead 
from  the  metallic  lead  electrodes  in  an  electrolytic  cell.  White  lead, 
or  technically  the  basic  lead  carbonate,  has  the  following  formula, 
which  is  sometimes  called  hydrate-carbonate  of  lead: 

2PbCO3.Pb(OH)2. 

For  our  purpose  we  will  require  either  a  rectangular  glass  jar  or 
cell,  or  else  a  large  beaker  glass,  and  heavy  sheet-lead  electrodes. 
The  adjustment  for  current  density  in  this  preparation  is  the  same 
for  both  electrodes,  that  is,  they  are  of  the  same  immersed  area  in 
the  electrolyte.  A  good  working  current  density  for  this  experiment 


ELECTROCHEMICAL   OPERATIONS.  123 

is  0.5  ampere  for  every  100  square  centimeters  of  anode  and 
cathode  surface  immersed.  The  expression  for  current  density  is 
frequently  met  with  in  abbreviated  ways,  which  the  reader  of  electro- 


FIG.  59. — Porous  Pots  of  Various  Shapes  and  Sizes  which  should  be  Supplied  to 
every  Electrochemical  Laboratory. 

chemical  processes  will  come  across,  and  they  are  therefore  given 
here  in  their  usual  manner,  in  order  that  he  may  become  familiar 
with  them.  For  example,  the  following  expression, 

Da  =  Dc  =0.5  ampere  per  100  square  centimeters, 

means  that  the  anode  current  density  is  the  same  as  the  cathode 
current  density,  and  that  they  each  equal  0.5  ampere  per  100  square 
centimeters  of  immersed  surface,  measuring  usually  both  sides  of 
the  two  electrodes  in  making  the  calculation  of  area.  The  expression 

N.D.ioo=o.5  ampere 

will  also  be  met  with,  expressing  the  current  flow  from  an  electrode 
for  every  100  square  centimeters  of  electrode  area. 

Let  us  now  prepare  a  few  grams  of  electrolytic  white  lead,  and 
tabulate  the  data  in  such  concise  form  that  we  should  at  any  time  be 
able  to  repeat  the  experiment  with  certainty,  or  be  able  to  direct 
others  to  do  so.  The  electrolyte  in  this  case  will  be  12  grams  of 
sodium  chlorate  and  3  grams  of  sodium  carbonate  dissolved  in  i  liter 
of  water.  A  rectangular  glass  cell,  two  sheet-lead  electrodes,  and  our 
lamp-bank  equipment  in  connection  with  a  lighting  circuit  will 
meet  the  electrical  requirements,  and  it  only  remains  to  fit  up  a 
generator  for  the  production  of  carbon-dioxide  gas  from  dilute 


124 


EXPERIMENTAL   ELECTROCHEMISTRY. 


acid  and  fragments  of  marble.  The  electrolysis  is  conducted  at 
about  20°  C.,  and  a  slow  current  of  carbon-dioxide  gas  is  led  into 
the  electrolyte  in  contact  with  the  cathode,  the  electrolyte  being 
kept  in  motion  by  a  stirrer.  The  white  lead  flows  down  in  thick 
clouds  from  the  anode  to  the  bottom  of  the  cell,  and  may  be  col- 
lected in  a  little  bag  of  tow  attached  to  the  electrode,  when  it  may 
be  removed  and  ground  with  oil  to  make  the  well-known  basis  for 
oil  colors.  The  yield  of  white  lead  in  this  experiment  is  excellent, 
and  the  operation  forms  a  very  pleasing  lecture  preparation,  for 
the  formation  and  falling  down  of  the  white  lead  from  the  solution 
is  very  beautiful  and  pleasing,  especially  when  one  is  familiar  with 
the  unattractive  old  Dutch  method,  dependent  upon  the  chemical 
action  of  the  vapors  of  acetic  acid,  carbonic  acid,  and  oxygen  upon 
masses  of  lead  in  pots,  which  must  be  buried  for  long  periods  of 
time  in  horse-manure,  in  order  that  fermentation  may  assist  chemi- 
cal action  by  an  increase  in  temperature.  Our  electrolytic  process 
may  be  made  continuous,  and  has  attained  commercial  importance 
in  recent  years.  In  this  experiment  the  electrolyte  contains  two 
salts  in  very  dilute  solution.  The  sodium  chlorate,  which  is  present 

in  four-fifths  of  the  total  amount,  has  as  an  anion  ClOs  which  forms 
a  soluble  salt  with  the  anode  lead,  producing  lead  chlorate,  which 

passes   into   solution.     The   sodium   carbonate,   whose   anion   CO 3 


FIG.  60.  FIG.  61. 

FlG.  60. — Experimental  Apparatus  for  the  Electrolytic  Production  of  White  Lead 
from  Lead  Electrodes. 

FlG.  61. — Experimental  Apparatus  for  the  Electrolytic  Preparation  of  Cadmium  Yel- 
low from  a  Stick  Cadmium  Anode. 

forms  an  insoluble  salt,  lead  carbonate,  produces  the  precipitation. 
As  a  result  of  using  such  proportions,  the  insoluble  salt  does  not 


ELECTROCHEMICAL   OPERATIONS.  125 

deposit  at  once  upon  the  anode,  but  is  precipitated  some  distance 
from  it,  and  does  not  give  trouble  by  forming  an  insoluble  crust  on 
the  ele'ctrode.  The  caustic  soda  produced  at  the  cathode  co- 
bines  with  the  carbon -dioxide  gas  which  is  bubbling  through  the 
solution,  and  regenerates  sodium  carbonate.  Fig.  60  will  make 
the  apparatus  clear.  Here  in  the  center  of  the  cell  is  shown  a  stirrer 
to  be  operated  by  a  small  electric  motor  when  it  is  desired  to  show 
the  experiment  in  the  lecture-room.  Below  will  be  found  tabulated 
the  principal  data  in  such  an  experimental  run: 

Duration  of  run i  hour 

Electrolyte 12   grams   NaClO3, 

3  grams  Na2CO3 
in  i  liter  water 

Character  of  apparatus See  figure 

Dimensions  of  cell 8  cm.X2o  cm.X2o  cm. 

Source  of  electricity Lighting     circuit     and 

lamp-bank 

Temperature  of  electrolyte 20°  C. 

Amperes  flowing 0.5  ampere 

Volts  indicated 60 

Area  of  anode  immersed 100  sq.  cm. 

Area  of  cathode  immersed.  . 100  sq.  cm. 

Current  density  at  anode N.D.100  =  o. 5  ampere 

Current  density  at  cathode N.D.100  =  o.5  ampere 

Distance  between Approximately  18  cm. 

Material  of  anode Soft  sheet  lead 

Material  of  cathode Soft  sheet  lead 

Phenomenon  at  anode White      lead      flowing 

down  in  streams 

Phenomenon  at  cathode Bubbling  of  carbon  di- 
oxide gas  and  the 
formation  of  Na2CO3 

Another  plan  for  producing  a  carbonate  of  lead  can  be  shown 
with  this  same  piece  of  apparatus,  but  with  a  different  electrolyte. 
A  solution  of  sodium  nitrate  is  used,  which  when  electrolyzed  forms 
nitric  acid,  which  attacks  the  lead  electrode  and  puts  it  into  solution 
as  lead  nitrate.  The  following  equations  show  how  this  scheme 
probably  works : 

1.  NaNO3  +  H2O=NaOH  +  HNO3. 

2.  2HNO3  +  Pb=Pb(NO3)2 

3.  Pb(NO3)2  +  2NaOH 

4.  Pb(OH)2  +  HNaC03=PbC03  +  NaOH  +  H 


126  EXPERIMENTAL  ELECTROCHEMISTRY. 

Instead  of  reactions  i  and  2  taking  place  as  shown,  the  following 
may  be  the  true  state  of  affairs,  since  hydrogen  is  liberated  at  the 
cathode : 

2NaN03  +  2H20  +  Pb  =  (2NaOH  +  H2)  +  PbO2  +  (NO3)  2. 

Equation  4  results  from  the  addition  to  the  lead  hydroxide  of 
a  solution  of  sodium  bicarbonate.  Other  modifications  of  this 
very  beautiful  method  will  doubtless  suggest  themselves  to  the  in- 
genious student,  apart  from  the  interesting  quantitative  figures 
he  is  in  a  position  to  obtain  by  working  with  such  an  equipment 
and  electrical  measuring  instruments.  Of  course,  for  economy  in 
operation  the  motor-generator  should  be  used,  as  we  do  not  require 
the  electric  current  at  anything  like  no  volts  pressure. 

Having  produced  the  white  lead,  which  is  the  basis  for  most 
oil-color  paint,  we  can  next  try  our  hand  at  the  electrolytic  pro- 
duction of  pigments.  Perhaps  the  easiest  and  most  satisfactory 
pigment  to  take  up  first  is  that  of  cadmium  yellow. 


THE   ELECTROLYTIC   PRODUCTION   OF   CADMIUM   YELLOW. 

This  very  brilliant  and  beautiful  pigment  may  be  easily  pro- 
duced electrolytically  in  a  cell  similar  to  that  employed  in  the  prepa- 
ration of  white  lead.  This  cell  is  shown  in  Fig.  61,  a  cylindrical 
stick  or  rod  of  cadmium  acting  as  the  anode,  and  a  strip  of  platinum 
acting  as  the  cathode.  In  the  place  of  the  CO 2  generator  as  used 
in  the  previous  preparation,  a  hydrogen-sulphide  generator  is  em- 
ployed. For  this  purpose,  as  is  well  known  by  every  chemist,  we 
require  some  fragments  of  iron  sulphide  and  a  little  dilute  hydro- 
chloric or  sulphuric  acid.  This  generator  is  depicted  in  its  simplest 
form,  and  may  be  replaced  to  advantage  by  one  of  the  approved 
" automatic"  types,  whereby  the  supply  of  gas  controls  the  action 
of  the  acid  upon  the  iron  sulphide.  The  electrolyte  in  this  experi- 
ment consists  of  a  saturated  solution  of  common  salt  in  water,  and 
when  electrolyzed  under  these  conditions  forms  cadmium  chloride 
at  the  anode,  and  sodium  hydroxide  at  the  platinum  cathode.  For 
the  production  of  any  quantity  of  this  pigment,  both  the  anode 
and  cathode  should  be  placed  in  porous  pots  to  prevent  the  mixing 


ELECTROCHEMICAL   OPERATIONS.  127 

together  of  the  respective  electrode  products.  The  cadmium  chloride 
produced  is  immediately  precipitated  as  the  brilliant  yellow  cad- 
mium sulphide  by  the  stream  of  hydrogen-sulphide  gas.  The 
following  simple  equations  indicate  the  steps  in  the  production  of 
the  pigment: 

2NaCl  +  2H2O  =  2NaOH  +  C12, 
2Cd  +  C12  +  2H2S  =  2CdS  +  2HC1. 

If  the  electrolyte  is  kept  stirred  by  a  mechanical  device,  the 
effect  is  very  beautiful  indeed.  The  tabulation  of  the  data  in  the 
electrolytic  preparation  of  cadmium  yellow  is  given  below: 

Duration  of  run i  hour 

Electrolyte Saturated  solution  of  NaCl 

in  water 

Character  of  apparatus See  figure 

Dimensions  of  cell 8  cm.X2o  cm.X2o  cm. 

Source  of  electricity Lighting  circuit  and  lamp- 
bank,  except  for  econ- 
omy and  quantitative 
work.  Then  use  motor- 
generator. 

Temperature  of  electrolyte 30°  C. 

Amperes  flowing i  .00  ampere 

Volts  indicated -.  4.5 

Area  of  anode  immersed 50  sq.  cm. 

Area  of  cathode  immersed 100  sq.  cm. 

Current  density  at  anode N.D.100  =  2  amperes 

Current  density  at  cathode N.D.100=  i  ampere 

Distance  between Approximately  18  cm. 

Material  of  anode Rod  or  stick  of  cadmium. 

Material  of  cathode Strip  of  platinum 

Phenomenon  at  anode Solution  of  CdCl2 

Phenomenon  at  cathode Liberation    of   hydrogen 

and  the  formation  of 
NaOH 

Phenomenon  between The  precipitation  of  CdS 

Special  peculiarities^ Use  of  porous  pots  for  the 

production  of  the  pure 
pigment  in  quantity  to 
prevent  mixing  of  elec- 
trode products. 

Note  here  the  double  current  density  at  the  anode  as  expressed 
in  the  abbreviated  manner,  as  the  result  of  using  a  stick  of  cad- 


128 


EXPERIMENTAL   ELECTROCHEMISTRY. 


mium  having  one-half  the  area  of  the  platinum  strip.     The  next 
pigment  is  that  of  mercury  vermilion  described  as  follows: 


THE   ELECTROLYTIC   PRODUCTION   OF   MERCURY   VERMILION. 

The  electrolytic  production  of  this  brilliant  sulphide  is  a  little 
more  difficult  to  accomplish,  as  the  conditions  must  be  exactly 
right  or  the  scheme  does  not  work  out  as  smoothly  as  that  for  the 
preparation  of  the  cadmium  sulphide.  Fig.  62  shows  the  arrange- 


FIG.  62. — Experimental  Apparatus  for  the  Electrolytic  Preparation  of  Mercury  Ver- 
milion from  a  Mercury  Anode. 

ment  of  the  apparatus,  where  a  mass  of  mercury  acting  as  anode 
is  shown  within  a  small  porcelain  dish,  with  a  strip  of  platinum 
as  cathode.  This  little  dish  may  rest  upon  a  block  of  glass,  as  for 
example  a  rectangular  glass  paper-weight,  for  effect,  if  shown  to 
a  number  of  persons  as  a  lecture  experiment.  A  platinum  wire 
runs  down  into  the  mercury,  and  is  protected  by  a  covering  of  thin 
rubber  tubing  to  prevent  its  acting  as  an  electrode.  A  hydrogen- 
sulphide  generator  similar  to  that  used  in  the  preparation  of  the 
cadmium  sulphide  is  employed,  as  shown  at  the  right.  The  electro- 
lyte consists  of  a  solution  of  8  per  cent  each  of  ammonium  and  sodium 
nitrates, 

NH4NO3  and  NaNO3, 

which  electrolyze  into  NH4OH  and  NaOH  at  the  cathode,  and  the 
setting  free  of  the  two  corresponding  NO3  groups  at  the  anode, 
which  is  of  mercury,  and  consequently  the  soluble  mercury  nitrate 
is  formed,  Hg(NO3)2.  The  hydrogen  sulphide  acting  upon  the 
nitrate  of  mercury  produces  the  sulphide 

Hg(N03)  2 + H2S  =  HgS  +  2HN03, 


ELECTROCHEMICAL  OPERATIONS.  129 

with  the  formation  of  two  molecules  of  nitric  acid,  which,  acting 
upon  the  ammonium  and  sodium  hydroxides,  reforms  ammonium 
and  sodium  nitrate. 

NaOH  +  HNO3  =  NaNO3  +  H2O, 
NH4OH  +  HN03  =NH4N03  +  H20. 

The  following  tabulation  shows  the  important  points  to  observe 
in  the  successful  preparation  of  this  vermilion  electrolytically : 

Duration  of  run i  hour 

Electrolyte 8  grams  NH4NO3,  8 

grams  NaNO3  in  i 
liter  of  water 

Character  of  apparatus See  figure. 

Dimensions  of  cell 8  cm.X2o  cm.Xao  cm. 

Source  of  electricity Motor-generator 

Temperature  of  electrolyte 50°  C. 

Amperes  flowing 5  amperes 

Volts  indicated 5.5  volts 

Area  of  anode  immersed 200  sq.  cm.  approx. 

Area  of  cathode  immersed 100  sq.  cm. 

Current  density  at  anode N.D.UK)  =  2  .5  amperes 

™"  Current  density  at  cathode N.D.100  =  5  amperes 

Distance  between 12  cm.  approximately 

Material  of  anode Metallic  mercury  (see  il- 
lustration) 

Material  of  cathode Strip  platinum 

Phenomenon  at  anode Formation  of  Hg  (NO3)2 

Phenomenon  at  cathode Production    of    NH4OH 

and  NaOH 

Special  peculiarities Arrangement  of  mercury 

in  small  porcelain  dish 

For  an  effective  lecture  exhibit  the  vermilion  sulphide  should  be 
agitated  by  means  of  a  mechanical  stirrer.  Fig.  63  illustrates  four 
electrolytic  cells  in  series  with  electric  motors  attached  to  stirrers, 
producing  a  very  striking  apparatus  for  the  simultaneous  production 
of  white  lead  and  pigments.  It  is  absolutely  necessary  to  insulate 
the  stirrer  jods  from  the  shafts  of  the  motors  if  a  common  electric- 
lighting  circuit  and  lamp-bank  is  employed  for  power  for  the 
motors  and  electrolyzing  current.  If  this  is  not  carefully  done, 
there  will,  with  most  of  the  small  motors  on  the  market,  be  trouble- 
some short  circuits,  and  a  failure  to  accomplish  the  electrolysis  from 
this  cause.  These  motors  may  be  joined  in  series,  and  the  cells 


130 


EXPERIMENTAL  ELECTROCHEMISTRY. 


should  be  mounted  upon  a  board,  which  may  be  lowered  by  remov- 
ing the  support  in  order  to  withdraw  the  electrodes  and  stirrers. 


FIG.  63. — Arrangement  of  Electrolytic  Cells  with  Electromechanical  Stirrers  for  the 
Experimental  Preparation  of  White  Lead  and  Colored  Pigments  Simultaneously. 
This  apparatus  is  designed  as  a  striking  lecture-room  experiment.  It  is  necessary 
to  insulate  the  stirrer  rods  with  hard-rubber  connections  as  indicated  in  black  if 
a  common  electric -lighting  circuit  is  employed  for  motors  and  electrolysis. 

It  is  almost  needless  to  say  that  this  piece  of  apparatus  will  be  also 
useful  for  any  other  operations  where  mechanical  agitation  is  re- 
quired for  prolonged  periods  of  time.  There  are  other  pigments 
which  may  be  easily  produced  in  the  same  general  manner,  the 
details  of  which  will  be  left  to  the  ingenuity  of  the  student.  For 
example,  a  beautiful  green  may  be  produced  electrolytically  as 
follows : 


THE  ELECTROLYTIC  PRODUCTION  OF  SCHEELEJS  GREEN. 

For  this  preparation  dissolve  10  grams  of  sodium  sulphate  in 
i  liter  of  distilled  water  and  place  in  the  electrolytic  cell  as  employed 
for  the  previous  compounds.  The  electrodes  are  cut  from  pure 
soft  sheet  copper  about  5  centimeters  by  25  centimeters  for  the  size 


ELECTROCHEMICAL   OPERATIONS. 


of  cell  we  are  using,  and  about  No.  18  gauge.  The  cell  and  electro- 
lyte must  be  heated  to  a  temperature  of  about  100°  C.  by  means  of 
a  water-bath.  A  little  bag  of  tow  is  made  and  filled  with  white 
arsenious  oxide,  which  is  suspended  in  the  electrolyte.  A  current 
of  about  3  amperes  is  necessary  for  a  cell  of  this  size,  and  it  is  better 
to  employ  the  lighting  current  and  the  lamp-bank  for  the  electrolyzing 
current.  Copper  sulphate  and  sodium  hydroxide  are  formed,  the 
sodium  hydroxide  dissolving  the  arsenious  oxide  and  forming  sodium 
arsenite.  The  sodium  arsenite  immediately  reacts  with  the  copper 
sulphate  which  separates  as  a  beautiful  green  precipitate  to  form  the 
copper  arsenite,  regenerating  sodium  sulphate.  The  operation  may  be 
conducted  until  the  copper  electrodes  are  consumed,  and  the  arsen- 
ious oxide  completely  converted  to  the  arsenite  of  copper. 


THE   ELECTROLYTIC    PRODUCTION   OF   PRUSSIAN   BLUE. 

In  the  same  general  manner  Prussian  blue  may  be  prepared  in 
the  electrolytic  cell.  A  potassium  ferrocyanide  solution  of  10 
grams  to  the  liter  is  precipitated  by  means  of  a  normal  ferrous 
salt  solution.  This  precipitate  is  stirred  in  water  by  means  of  our 
mechanical  stirrer.  This  must  be  placed  in  a  large  porous  pot  of 
sufficient  diameter  to  admit  a  suitable  stirrer  in  which  a  platinum 
anode  is  placed  About  25  cubic  centimeters  of  nitric  acid  is  added 
to  the  solution  in  the  pot  and  a  platinum  cathode  is  placed  outside. 
About  5  amperes  must  be  passed  through  the  system  for  several 
hours,  when  we  will  obtain  for  our  product  a  dark  Berlin  blue. 

A  few  words  concerning  experimental  apparatus  may  be  of  ser- 
vice to  the  electrochemist.  Fig.  64  illustrates  a  most  convenient 
and  satisfactory  electrolytic  stand  for  a  great  variety  of  purposes. 
The  column  is  solid  glass,  which  serves  to  mount  the  two  electrode 
arms  and  effectually  insulate  them  from  each  other.  The  electrode 
arms  not  only  slide  up  and  down  the  column  and  are  set  by  means 
of  a  thumb-screw,  but  the  electrodes  may  be  slid  in  and  out  from 
the  center  of  the  column  and  set  at  any  required  distance.  For 
rapid  adjustment  and  flexibility  of  use  these  stands  are  unsurpassed. 
A  half  dozen  or  more  of  these  stands  should  be  a  part  of  every  electro- 
lytic equipment.  They  are  always  ready  to  receive  electrodes  of 
various  kinds  and  materials,  and  are  quickly  connected  to  the  source 


I32 


EXPERIMENTAL   ELECTROCHEMISTRY. 


of  electricity  by  means  of  binding  screws.     Many  electrochemical 
investigations   may   be   begun  by   electrolyzing  small   volumes   of 


FIG.  64. — Convenient  Electrolytic  Stand  for  Conducting  Experimental  Work.  The 
column  is  of  solid  glass,  and  the  electrodes  are  easily  adjusted  for  cells  and  beakers 
of  various  kinds. 

electrolytes  in  beakers  with  these  stands  until  data  warranting  the 
use  of  larger  cells  with  separately  fixed  electrodes  are  secured. 


CHAPTER   IX. 

ELECTROLYTIC  PREPARATION  OF  POTASSIUM  CHLORATE 
FROM  POTASSIUM  CHLORIDE.  PREPARATION  OF  SOLII> 
TRIOXIDE  OF  SULPHUR.  PRODUCTION  OF  OZONE  FROM 
THE  ATMOSPHERE.  EXPERIMENTS  WITH  OZONE  AND  ITS 
PRACTICAL  APPLICATIONS. 

ELECTROLYTIC   PREPARATION   OF   POTASSIUM   CHLORATE. 

AN  outline  of  the  purely  chemical  method  for  preparing  this 
important  compound  should  be  given  before  undertaking  the  elec- 
trolytic plan.  Potassium  chlorate,  or  chlorate  of  potash,  is  prepared, 
in  the  chemical  way  by  passing  an  excess  of  chlorine  gas  rapidly 
into  a  strong  solution  of  potassium  hydroxide.  When  the  liquid 
becomes  hot  enough  to  decompose  the  hypochlorite  first  formed  into* 
potassium  chloride,  which  remains  in  solution,  the  potassium  chlorate 
deposits  in  tabular  crystals.  The  ultimate  result  of  such  a  chemical 
method  for  this  compound  may  be  expressed  by  the  following 
equation : 

6KOH  +  C16  =  KC1O3  +  5KC1  +  3H2O. 

If  potassium  carbonate  or  a  weak  solution  of  potassium  hydroxide 
be  employed,  the  liquid  will  require  boiling  after  saturation  with 
chlorine,  in  order  to  convert  the  hypochlorite  into  chlorate.  This 
chemical  process  for  the  preparation  of  potassium  chlorate  is  far 
from  being  economical,  since  five-sixths  of  the  potash  is  converted 
into  chloride,  being  employed  merely  to  furnish  oxygen  to  convert 
the  chlorine  into  chloric  acid.  In  manufacturing  potassium  chlorate 
upon  a  large  scale,  a  much  cheaper  material  is  used,  namely  lime,  ta- 
furnish  the  oxygen.  The  lime  is  mixed  with  water,  and  saturated 
with  chlorine  gas  in  closed  leaden  tanks,  when  we  obtain  the  following- 
reaction  : 

2Ca(OH)  2  +  4C1  =  Ca(OCl)  2  +  CaCl2  +  H2O. 

133 


T34  EXPERIMENTAL    ELECTROCHEMISTRY. 

The  liquid  is  boiled  down,  when  the  calcium  hypochlorite  is  decom- 
posed into  calcium  chlorate  and  chloride, 


The  calcium  chlorate  is  now  decomposed  by  boiling  with  potassium 
chloride,  when  it  yields  calcium  chloride  which  remains  in  solution, 
and  potassium  chlorate  which  separates  in  crystals  as  the  solution 
cools.  Tne  following  equation  expresses  this  step  in  the  process: 

Ca(C103)  2  +  2KC1  =  CaCl2  +  2KC1O3. 

In  the  preparation  of  potassium  chlora  e  by  electrolytic  means, 
certain  difficulties  are  met  with.  The  simple  plan  of  subjecting  a 
Iiot  solution  of  potassium  chloride  to  electrolysis,  and  allowing  the 
free  mixing  of  the  chlorine  and  caustic  soda  produced,  is  workable 
only  with  low  concentrations.  To  obtain  the  potassium  chlorate 
from  an  electrolyte  containing  chloride  is  a  rather  difficult  matter 
"by  means  of  any  process  of  crystallizing  out.  Without  a  porous 
partition  or  means  of  keeping  the  electrode  products  separated,  the 
anode  or  oxidized  product  will  reach  the  cathode  and  will  there  be 
reduced.  At  the  same  time  the  potassium  hydroxide  formed  at  the 
cathode  can  serve  independently  as  an  electrolyte,  yielding  at  the 
•electrodes  oxygen  and  hydrogen  gases,  with  the  useless  expenditure 
of  electrical  energy.  The  student  in  electrochemical  processes 
should  be  on  the  lookout  for  every  such  possibility,  and  should  have 
such  losses  in  mind  in  the  design  and  construction  of  his  apparatus. 
Let  us  take  up  the  experimental  preparation  of  this  most  important 
compound  electrolytically  in  the  simplest  manner,  using  first  an  open 
beaker  glass  without  porous  partitions  The  student  can  make  his 
determinations,  and  then  modify  the  apparatus  with  a  porous  pot 
with  a  view  to  increasing  the  working  efficiency.  For  the  simplest 
workable  plan  we  will  employ  an  electrolyte  of  the  following  composi- 
tion : 

100  grams  of  potassi  m  chloride, 
i  gram   of  potassium  carbonate, 
i  gram   of  potassium  dichromate, 

250  grams  of  hot  distilled  water. 

Tig.  65  shows  the  arrangement   of  the  necessary  apparatus  in  its 


POTASSIUM   CHLORATE.  135 

simplest  form.  In  making  records  of  experiments  in  note  books,  it 
cannot  be  too  strongly  impressed  upon  the  student  to  make  concise 
and  neat  little  sketches  of  the  apparatus  and  the  manner  in  which  it 
was  assembled,  to  be  accompanied  of  course  by  a  full  tabulated  list  of 
conditions  as  set  forth  in  a  previous  chapter.  In  our  first  illustration 
we  have  a  large  beaker  resting  upon  a  square  of  asbestos,  supported 
by  a  low  iron  ring  tripod  over  a  special  low  type  of  Bunsen  burner 
for  maintaining  the  electrolyte  at  such  an  elevated  temperature,  as 
is  necessary.  The  anode  and  cathode  are  both  of  sheet  platinum, 


FIG.  65. — Experimental  Apparatus  for   the  Electrolytic   Preparation  of    Potassium 
Chlorate  from  Potassium  Chloride. 

and  are  most  conveniently  supported  by  a  couple  of  electrolytic 
stands  with  insulating  glass  columns,  as  described  and  recommended 
in  the  last  chapter.  A  thermometer  is  immersed  in  the  electrolyte 
together  with  a  glass  tube  as  indicated,  through  which  a  current  of 
carbon-dioxide  gas  is  passed.  The  current  density  at  the  anode 
should  be  at  least  20  amperes  per  100  square  centimeters  of  immersed 
electrode,  and  the  current  density  at  the  cathode  should  be  about 
double  this  for  best  results.  The  electrolyte  is  kept  at  a  temperature 
of  60°  C.  and  a  feeble  acid  reaction  is  maintained  by  a  current  of  car- 
bon-dioxide gas,  which  also  keeps  the  solution  agitated  and  of  uniform 
composition.  According  to  Dr.  Karl  Elbs,"of  the  University  of  Giessen, 
at  least  60  ampere  hours  are  necessary  for  this  quantity  of  electro- 
lyte, since  one  ampere  hour  yields  0.75  gram  of  potassium  chlorate. 
According  to  Dr.  Elbs,  if  a  separation  of  potassium  chlorate  has 


'36 


EXPERIMENTAL   ELECTROCHEMISTRY. 


commenced  during  the  electrolysis,  after  allowing  the  electrolyte  to 
cool  down,  a  considerable  quantity  of  potassium  chlorate  crys- 
tallizes out,  which  is  purified  by  a  single  recrystallization.  By 
evaporation  of  the  mother  liquor  to  about  one-half  its  original  volume 
and  then  allowing  it  to  cool  down,  a  second  lot  of  crystals  is  obtained. 
The  current  efficiency  amounts  to  about  70  per  cent  of  the  theoretical, 
and  only  begins  to  fall  off  to  a  serious  extent  if  over  50  per  cent  of  the 
potassium  chloride  has  been  converted  into  potassium  chlorate.  It 
is  very  evident  from  the  foregoing  that  if  the  current  efficiency  be 

calculated  from  the  amount  of  potassium 
chlorate  in  the  crystalline  solid  form,  the 
figure  obtained  will  be  too  low  because 
of  the  quantity  remaining  behind  in  the 
mother  liquor.  Sodium  chlorate  may  be 
prepared  with  the  same  apparatus  by  using 
as  an  electrolyte, 

80  grams  of  sodium  chloride, 
2  grams  of  sodium  carbonate, 
i  gram  of  sodium  dichromate, 
250  grams  of  hot  distilled  water. 

The  electrical  conditions  are  the  same  as 
in  the  preparation  of  potassium  chlorate 
and  the  current  efficiency  is  also  about 
70  per  cent.  The  electrolyte  in  this  case 
is  evaporated  to  a  small  volume,  when 
the  sodium  chloride  will  separate  out  of 

FIG.  66.-Useful  Design  of  U    ^     solution     and    js    filtered     off.        The 
Tube  for  Conducting  Elec- 
trolytic    Preparations     and    final     Product     IS     not     pure,     being    COn- 

Maintaining    an    Elevated  taminated     with     sodium    chloride     and 
Temperature  by  the  Current  sodium  chromate.      Sodium    chromate  is 

Itself.      The    center    tube  ,.      ,          ,    ,  ,  ,  - 

receives  the  thermometer.      exceedingly  soluble,  and  a  complete  pun- 
fication    is    therefore    a   difficult    matter. 

Potassium  and  sodium  chlorates  may  be  quickly  prepared  in  small 
quantities  without  the  aid  of  external  heating  by  employing  a  special 
U  tube  with  a  center  limb  like  that  illustrated  in  Fig.  66.  Because 
of  the  comparatively  small  cross-section  of  the  electrolyte,  the  tempera- 
ture can  easily  be  kept  at  the  required  point  by  controlling  the  electric 


PREPARATION   OF  SOLID   TRIOXIDE   OF  SULPHUR.          137 

current.  The  central  tube  serves  for  the  reception  of  the  thermometer. 
Such  a  piece  of  apparatus  not  only  serves  for  this  particular  line  of 
electrolytic  work,  but  is  of  a  generally  useful  and  flexible  character. 
Fig.  67  illustrates  such  a  tube  in  connection  with  an  ammeter  and 


FIG.  67. — Combination  of  Special  U  Tube  with  Ammeter  and  Lamp-bank,  where- 
by Electrolytes  can  be  Maintained  at  their  Boiling-points  by  the  Electrolyzing 
Current.  By  means  of  the  ammeter  and  the  thermometer  conditions  can  be 
easily  controlled. 

lamp-bank,  by  means  of  which  electrolytes  can  easily  be  maintained 
at  their  boiling-points  by  the  electrolyzing  current  if  necessary. 


PREPARATION  OF   SOLID   TRIOXIDE  OF   SULPHUR. 

It  will  be  remembered  that  in  a  previous  chapter  the  electrolysis 
of  concentrated  sulphuric  acid  was  conducted  with  the  liberation  of 
hydrogen,  oxygen,  ozone,  and  free  sulphur,  and  at  elevated  tempera- 
tures the  electrode  products  become  hydrogen,  oxygen,  and  sulphur 
trioxide.  If  now  we  select  a  thin  glass  Woulf  bottle  intended  for  heat- 
ing, and  subject  concentrated  sulphuric  acid  to  a  process  of  electrolysis 
with  a  heavy  current,  we  will  elevate  the  temperature  sufficiently  to 
produce  sulphur  dioxide  in  quantity,  which  may  be  condensed  to  a 
white  solid  with  ease  by  passing  the  gas  into  a  suitable  condenser. 
This  experiment  is  not  intended  to  show  a  method  for  preparing 
sulphur  trioxide,  to  compete  with  any  existing  chemical  schemes, 


138 


EXPERIMENTAL   ELECTROCHEMISTRY. 


but  merely  as  an  exercise  of  interest  in  conducting  practical  work. 
Fig.  68  shows  the  arrangement  of  the  apparatus,  which  consists  of  a 
thin  Woulf  bottle  with  platinum  electrodes  and  a  thermometer  for 
noting  the  temperature.  There  is  a  glass  tube  leading  to  a  condenser 
fitted  with  stop-cocks  immersed  in  a  freezing-mixture,  and  a  lamp- 
bank  for  modifying  the  lighting  current.  Electrical  measuring  instru- 
ments are  shown  in  this  illustration,  although  the  production  of  this 
interesting  compound  upon  this  plan  hardly  warrants  the  setting 
down  of  efficiency  data.  Like  the  experiment  with  the  cold  acid, 


FIG.  68. — Experimental  Preparation  of  Solid  Sulphur  Trioxide  by  the  Electrolysis  of 
Concentrated  Sulphuric  Acid. 

the  experiment  is  useful  in  demonstrating  the  composition  of  sul- 
phuric acid  by  electrolytic  means.  Such  a  piece  of  apparatus  is 
very  useful  in  conducting  research  work  upon  compounds  when  the 
mechanism  of  electrolysis  is  doubtful.  For  example,  in  electrolysis 
we  may  be  obtaining  a  condensible  gas  from  one  of  the  electrodes, 
and  it  would  be  highly  desirable  to  obtain  this  gas  in  a  liquid  or  a 
solid  form  for  identification.  In  a  certain  piece  of  research  work 
undertaken  by  the  author,  oxides  of  nitrogen  were  given  off  on  elec- 
trolys's,  and  it  was  convenient  to  pass  the  electrode  gas  through  such 
a  condenser  immersed  in  liquid  air,  when  the  oxides  of  nitrogen  con- 


THE   ELECTRICAL   PRODUCTION   OF   OZONE. 


139 


densed  to  a  light-blue  solid,  and  were  estimated  in  this  form.  Sul- 
phur dioxide,  as  is  well  known  by  all  general  chemists,  can  be  lique- 
fied by  passing  it  through  such  a  condenser  immersed  in  a  simple 
freezing- mixture  of  ice  and  salt.  It  is  believed  that,  apart  from 
introducing  an  experiment,  or  a  method  of  preparing  a  compound, 
the  description  of  special  and  useful  apparatus  will  prove  as  valuable 
to  the  experimenter  and  investigator  as  many  theories  and  their 
applications.  Having  produced  a  number  of  typical  electrolytic 
preparations  in  inorganic  chemistry,  we  would  neglect  some  very 
important  applications  of  electricity  to  chemistry,  unless  we  prepared 
certain  important  gases  of  commercial  value. 
Perhaps  the  first  gaseous  preparation  should  be 
that  of  ozone,  and  the  following  pages  will 
therefore  be  devoted  to  this  valuable  product. 

THE   ELECTRICAL   PRODUCTION   OF   OZONE. 

Ozone  is  the  chemical  name  applied  to  a 
peculiar  form  of  oxygen  the  exact  nature  of 
which  is  open  to  some  little  discussion,  as  it 
has  been  impossible  to  obtain  absolutely  pure 
ozone.  It  is  always  accompanied  with  ordinary 
oxygen,  but  there  are  good  reasons  for  believ- 
ing that  ozone  consists  of  three  atoms  of  oxygen. 
Three  atoms  of  oxygen,  occupying  three  vol- 
umes, therefore,  combine  to  one  molecule  of 
ozone  which  occupies  two  volumes.  Ozone,  FlG-  69-  —  Experimental 

,.  .  .  ,  ,.   ,.  .  ,  .         Apparatus  for  the  Pro  - 

according  to  this  scheme  of  formation,  would      duction  of  Ozone  from 


the  Atmosphere.  Dilute 
sulphuric  acid  fills  both 
outside  cylinder  and  in- 
ner chamber  of  the  cen- 
tral tube. 


be  one-half  as  heavy  again  as  ordinary  oxygen, 

and  experiments  upon  its  rate  of  diffusion  go 

to  support    this  theory.     In    the    year    1785, 

A^on    Marum    noticed     that     oxygen     upon 

being    subjected    to   electrical    discharges,  acquired    an   odor   like 

that  experienced  after  the  atmosphere  had  been  subjected  to   an 

active    electrical    storm.     In    1840,    Schoenbein   called  attention  to 

the   similarity   between  the  odors  produced  when   air  was   treated 

to   electrical  discharges,   and  the  odors  noticed  when  water  was 

electrolyzed  between  platinum  electrodes,  or  gold  electrodes,  for  with 

the  baser  meta]s  the  production  of  ozone  was  not  so  marked.     The 


140  EXPERIMENTAL   ELECTROCHEMISTRY. 

production  of  ozone  was  probably  just  as  great,  only  it  was  largely 
expended  in  oxidizing  the  electrodes  when  they  were  not  of  platinum 
or  of  gold.  The  same  investigator  also  observed  that  a  like  odor 
accompanied  the  slow  oxidation  of  phosphorus,  and  also  of  sulphur, 
and  that  in  each  case  a  piece  of  filter-paper  moistened  with  a  solution 
of  starch  and  potassium  iodide  was  turned  blue.  About  the  same 
time,  two  other  investigators,  Marignac  and  De  la  Rive,  showed 
that  ozone  was  only  a  changed  condition  of  oxygen.  In  1852, 
Becquerel  and  Fremy  demonstrated  that  pure  oxygen  could  be 
converted  into  ozone.  In  1860,  Andrews  and  Tait  called  attention 
to  the  fact  that  a  marked  contraction  in  volume  accompanied  the 
formation  of  ozone  from  oxygen,  and  in  the  same  year  Soret  showed 
that  oil  of  turpentine  absorbed  ozone  completely,  and  in  this  way 
determined  its  relative  density,  confirming  his  results  in  1867  by  the 
method  based  on  the  rate  of  the  diffusion  of  gases  as  already  men- 
tioned. Andrews  suggested  at  this  time  that  the  substance  present 
in  the  atmosphere  which  affected  starch  and  potassium  iodide  paper 
was  this  modified  form  of  oxygen.  We  have  already  seen  that  ozone 
may  be  obtained  in  the  electrolysis  of  concentrated  sulphuric  acid 
between  platinum  electrodes.  Is  this  the  most  efficient  and  econom- 
ical way  of  producing  it?  It  is  not,  for  there  have  been  designed 
and  put  into  practice  many  forms  of  special  ozone-generators  of 
greater  efficiency.  For  laboratory  purposes  the  generator  as 
illustrated  in  Fig.  69  has  proven  very  useful.  Here  the  apparatus 
is  shown  in  section  in  order  that  its  several  parts  and  their  relations 
may  be  clearly  seen  and  understood.  The  tall  outside  cylinder  glass 
is  filled  with  dilute  sulphuric  acid,  one  to  ten,  as  well  as  the  inner 
chamber  of  the  tube  which  is  immersed  therein.  Two  platinum 
wires  are  dipped  respectively  into  the  acid  in  the  outer  glass  cylinder, 
and  in  the  acid  in  the  inner  tube.  When  these  platinum  wires  are 
connected  to  the  secondary  terminals  of  a  good  induction-coil,  the 
two  portions  of  the  sulphuric  acid  become  electrified,  and  there  is 
believed  to  be  a  stress  set  up  which  resolves  th$  oxygen  molecules 
into  its  atoms,  with  a  recombination  to  form  molecules  of  ozone. 
Dry  air  or  dry  oxygen  is  passed  through  the  space  between  the  two 
portions  of  acid,  which  space  for  most  economical  action  should  be 
as  narrow  as  possible.  Another  important  condition  is  the  tem- 
perature of  the  air  or  oxygen  used.  It  should  be  cooled  down  to  a 


THE   ELECTRICAL  PRODUCTION   OF  OZONE.  141 

low  temperature  before  sending  through,  and  should  not  be  supplied 
too  fast.     Fig.  70  illustrates  a  special  horizontal  form  of  ozone  ap- 


FIG.  70. — Another  Form  of  Ozone  Apparatus  Based  upon  the  Same  Principle.  The 
outer  and  inner  tubes  contain  dilute  sulphuric  acid.  The  inner  tube  is  sealed 
up,  only  a  small  air-bubble  remaining. 

paratus  based  upon  the  same  general  principle.  The  longer  the  tube 
and  the  greater  the  area  exposed  to  the  oxygen  or  air  the  greater  the 
ozonizing  power  of  the  apparatus  for  a  stream  of  air  or  oxygen  of 
a  given  velocity  and  volume.  The  ordinary  chemical  test  for  ozone, 
as  has  been  intimated,  is  a  damp  mixture  of  starch  and  potassium 
iodide,  preferably  made  into  test-paper.  To  make  a  good  test-paper 
for  our  work  with  ozone  preparation,  take  100  grams  of  starch 
and  grind  thoroughly  in  a  mortar  with  50  cubic  centimeters  of  distilled 
water.  The  thin  paste  is  then  poured  into  250  cubic  centimeters 
of  boiling  distilled  water  in  a  beaker,  and  one-half  a  gram  of 
potassium  iodide  crystals  are  added  and  made  to  dissolve  by  stirring. 
Narrow  pieces  of  filter-paper  are  drawn  through  this  solution  with 
glass  rods  and  hung  up  to  dry.  When  these  pieces  of  paper  are 
moistened,  and  exposed  to  ozone,  they  turn  blue,  but  are  not  affected 
by  ordinary  oxygen.  The  ozone  abstracts  the  potassium  from  the 
potassium  iodide,  and  sets  free  the  iodine,  which  has  the  specific 
property  of  imparting  a  deep-blue  color  to  starch.  Papers  impreg- 
nated with  manganese  sulphate,  lead  acetate,  or  thallous  oxide, 
become  brown,  in  the  first  two  cases  by  the  formation  of  the  peroxide 
of  the  metal,  and  in  the  last  case  from  the  formation  of  thallic  oxide, 
under  the  influence  of  ozone.  Thus  it  will  be  seen  that  ozone  is 
an  excellent  and  energetic  oxidizing  agent.  If  ozone  is  passed  into 
a  solution  of  indigo,  the  blue  color  will  soon  disappear,  since  the 
ozone  oxidizes  the  indigo,  and  gives  rise  to  products  which,  in  a 
diluted  state,  are  nearly  colorless.  Ordinary  oxygen  is  not  capable 
of  bleaching  indigo  in  this  manner.  If  ozone  is  passed  through  a 
tube  of  vulcanized  caoutchouc,  this  will  soon  be  perforated  by  the 


142 


EXPERIMENTAL   ELECTROCHEMISTRY. 


corrosive  effect  of  the  gas,  while  ordinary  oxygen  would  be  without 
effect  upon  it.  If  ozonized  air  be  passed  into  a  flask  with  a  little 
mercury  in  the  bottom,  the  surface  of  the  mercury  will  soon  be 
tarnished  as  the  result  of  the  formation  of  oxide,  and  when  the  mercury 
is  shaken  around  in  the  flask,  it  will  adhere  to  the  sides,  which  will 
not  be  the  case  with  pure  mercury,  as  is  well  known.  Let  us  look 
into  other  forms  of  ozone  apparatus  and  the  application  of  the 
electricity.  Fig.  71  illustrates  a  simple  Siemens  tube,  which  is 


FlG.  71. — Cross-section  and  Elevation  of  an  Original  Siemens  Apparatus  for  the 
Production  of  Ozone  from  Atmospheric  Oxygen.  The  sulphuric  acid  is  dis- 
placed in  this  tube  by  some  metal  not  readily  oxidized,  such  as  tinfoil. 

perhaps  the  simplest  to  construct  in  the  laboratory.  Here  we  have 
merely  an  inner  and  an  outer  tube  as  shown  in  the  sectional  view. 
The  inner  tube  is  held  in  position  by  a  good  cork  and  is  lined  on 
the  inside  with  tinfoil.  This  tube  is  closed  at  one  end  by  sealing 
off,  and  at  the  other  end  by  a  cork  stopper  through  which  a  platinum 
wire  passes  and  makes  contact  with  the  tinfoil  lining.  The  outer 
tube  has  a  side  and  end  tubulure  through  which  the  air  or  oxygen 
gas  is  passed.  This  outer  tube  is  coated  with  tinfoil  on  the  outside 
with  which  electrical  connection  is  also  made.  A  good  induction- 
coil  with  a  condenser  of  large  capacity  is  employed  with  this  apparatus 
as  with  the  acid  tubes.  In  a  lecture  by  Froelich  he  has  given  an 
account  of  the  experiments  which  have  been  made  in  the  laboratory 
of  Messrs.  Siemens  &  Halske  in  Berlin  for  the  commercial  production 
of  ozone.  The  original  Siemens  ozonizing  tube  was  like  that 
illustrated,  the  two  coatings  being  supplied  with  an  alternating 
current  of  high  potential,  while  oxygen  was  made  to  traverse  the 
annular  space  between  the  two  tubes.  It  appears  that  only  one 
dielectric  is  necessary,  mica,  celluloid,  porcelain,  and  the  like  being 


THE   ELECTRICAL  PRODUCTION   OF   OZONE.  143 

available,  as  well  as  glass,  and  the  ozone  tube  having  either  a  metal 
tube  within  and  a  metal-coated  non-conducting  tube  without,  or  a 
metal  tube  without,  while  the  inner  tube  is  made  of  the  non-con- 
ducting material  and  lined  with  metal.  The  metals  to  be  used  are 
of  course  those  which  are  not  attacked  by  ozone,  such  as  platinum, 
tin,  or  aluminium.  Cold  water  flows  through  the  inner  tube,  and 
through  the  annular  space  pure,  dry  air.  Several  such  tubes  may 
of  course  be  combined  into  one  system  and  be  worked  equally  well 
with  the  alternating  currents,  although  for  single  tubes  it  is  stated 
that  direct  currents  operated  by  interrupters  may  be  used  to  advan- 
tage. The  apparatus  as  described  by  Froelich  in  the  German 
laboratory  yields  2.4  milligrams  of  ozone  per  second.  Experiments 
have  been  made  with  a  view  of  producing  compressed  ozone  for 
technical  uses,  this  having  already  been  done  on  a  small  scale  under 
a  pressure  of  about  10  atmospheres.  One  use  of  ozone  especially 
dwelt  upon  by  Froelich  is  the  oxidation  of  organic  impurities  in 
drinking-water.  Experiments  with  ozone  upon  water-supplies  have 
been  made  in  this  country,  nevertheless,  for  a  long  time.  In  all 
productions  of  ozone  it  is  very  important  to  keep  the  temperature 
low,  and  the  following  experiment  will  serve  to  impress  this  fact 
upon  the  student:  If  ozone  be  made  to  pass  slowly  through  a  glass 
tube  heated  in  the  center  by  a  Bunsen  burner,  it  will  be  found  to 
lose  its  power  of  affecting  starch  and  potassium  iodide  paper,  the 
ozone  having  been  reconverted  into  ordinary  oxygen  under  the 
influence  of  heat.  The  formation  of  ozone  may  be  compared  with 
the  production  of  hydrogen  peroxide,  and  we  may  express  this  break- 
ing up  of  ozone  symbolically.  Just  as  hydrogen  dioxide,  H2O2, 
may  be  regarded  as  formed  by  the  combination  of  a  molecule  of 
water  H^O,  with  an  atom  of  oxygen,  so  ozone  may  be  viewed  as  a 
combination  of  a  molecule  of  oxygen  O2,  with  an  atom  of  oxygen. 
The  breaking  up  by  heat  of  ozone  may,  therefore,  be  expressed, 

2(002)=3(02). 

A  temperature  of  250°  C.  is  sufficient  to  completely  bring  about 
this  breaking  up  of  the  ozone.  As  we  have  learned,  a  given  volume 
of  oxygen  diminishes  when  a  portion  of  it  is  converted  into  ozone  by 
the  silent  electrical  discharge,  and  it  regains  its  original  volume 


144  EXPERIMENTAL   ELECTROCHEMISTRY. 

when  the  ozone  is  reconverted  by  heat.  It  is  of  interest  to  note  that 
the  conversion  of  oxygen  into  ozone  is  attended  by  the  absorption 
of  heat;  in  other  words,  it  is  endothermic.  The  value  of  this  heat 
absurption  may  be  expressed  thus : 

3O2  =  263  —  59,200  calories. 

Ozone  is,  therefore,  a  very  unstable  body  theoretically,  and  practically 
we  find  such  a  state  to  be  the  case.  To  work  any  one  of  the  ozonizers 
economically  in  the  laboratory  the  author  has  found  it  very  convenient 
and  satisfactory  to  first  dry  the  oxygen  or  air  by  passing  it  through 
concentrated  sulphuric  acid,  and  then  through  a  long  tin  or  lead 
worm  immersed  in  iced  water  Chilled,  dry  oxygen  of  course  gives  the 
richest  yield  of  ozone.  A  very  efficient  design  of  ozone-generator 
and  one  of  easy  manufacture  in  the  laboratory  is  illustrated  in  con- 
nection with  an  induction-coil  in  Fig.  72.  This  simply  consists  of 
a  large  outer  glass  tube  of  any  length,  containing  a  number  of  small 
thin- walled  glass  tubes  closed  by  sealing  off  at  one  end.  Narrow 
strips  of  tinfoil  are  pushed  into  each  tube,  as  indicated,  and  joined 
together  in  the  manner  of  connecting  up  an  electrical  condenser. 
A  stream  of  chilled,  dry  air  or  oxygen  is  passed  through  the  large 
tube.  Of  course  for  a  large  outer  tube  of  great  length  a  very 
powerful  induction-coil  must  be  employed.  The  adjustment  of  the 
size  and  len'gth  of  tube  to  the  induction-coil,  the  temperature,  dry- 
ness  and  rate  of  supply  of  air  or  oxygen,  etc.,  make  a  very  valuable 
set  of  conditions  for  the  student  to  experiment  with  with  a  view  to 
obtaining  a  combination  for  maximum  efficiency.  The  electrical, 
energy  supplied  to  the  coil  should  of  course  be  measured,  as  well  as 
every  other  chargeable  item  in  the  production  of  the  body  in  question. 
There  are  other  ways  of  producing  ozone  electrically,  although  in 
point  of  efficiency  they  cannot  be  compared  with  those  described 
Among  the  experiments  in  electrolysis  yielding  as  one  of  the  products 
ozone,  may  be  mentioned  the  electrolysis  of  aqueous  solutions  of 
nitric  acid,  hydrofluoric  acid,  sulphuric  acid,  and  phosphoric  acid, 
as  well  as  solutions  of  potassium  nitrate,  potassium  phosphate,  and 
sodium  sulphate.  Hydrochloric,  hydrobromic,  or  strong  nitric 
acid  do  not  produce  ozone  when  electrolyzed.  Neither  do  aqueous 
solutions  of  metallic  chlorides,  bromides,  iodides,  or  ferrous  sulphate. 


THE   ELECTRICAL  PRODUCTION   OF   OZONE.  145 

According  to  Houzean,  the  electrolysis  of  water  furnishes  only  3 
to  5  milligrams  of  ozone  per  liter.  When  a  given  quantity  of 
oxygen  is  subjected  to  the  action  of  charged  surfaces,  as  presented 
in  any  of  the  foregoing  descriptions  of  ozonizers,  only  one-fifth,  at 
most,  according  to  Bloxam,  is  converted  into  ozone ;  but  if  the  ozone 
be  now  removed  by  some  substance  which  absorbs  it,  a  fresh  quantity 
of  the  oxygen  may  be  ozonized.  The  proportion  of  ozone  formed 
depends  upon  many  conditions,  the  intensity  and  frequency  of  the 


FIG.  72. — Efficient  Type   of  Ozone   Apparatus  and   Induction-coil  Assembled   for 

Production. 

electrical  discharge,  the  pressure,  quantity,  temperature,  etc.  The 
question  of  temperature  in  all  ozone  processes  appears  to  be  by  far 
the  most  important.  According  to  the  older  researches,  about  the 
time  1880,  20  per  cent  of  the  oxygen  becomes  ozone  at  —25°  Co 
and  only  12  per  cent  at  20°  C.,  the  ordinary  working  temperature 
of  a  chemical  laboratory.  At  the  temperature  of  boiling  water,  the 
production  is  but  2  per  cent.  In  more  recently  made  determinations, 
1893,  it  is  stated  that  the  production  is  5.2  per  cent  at  20°  C.  The 
matter  of  ozone  production  has  occupied  the  minds  of  many  inventors 
during  the  last  few  years,  and  many  forms  of  commercial  apparatus 
have  been  designed  and  constructed  to  produce  this  gas  upon  a 
very  large  scale.  There  are  drum-shaped  chambers  containing 
many  sets  of  stationary  tinsel  brushes  arranged  around  the  cylindrical 
interior,  with  corresponding  revolving  sets  of  brushes  to  constitute 
the  opposite  pole,  for  example.  High  potential  discharges  of  vary- 
ing current  strength  have  been  experimented  with  in  such  pieces  of 


146  EXPERIMENTAL  ELECTROCHEMISTRY. 

apparatus,  and  it  has  been  found,  to  produce  the  best  effects,  that 
high  potential  difference  with  small  current  and  energy  value  must 
be  used.  Probably  this  is  due  to  the  absence  of  heating  effect  with 
electrical  discharges  of  small  quantity.  A  thick,  heavy  discharge 
appears  to  break  up  the  ozone  formed  almost  as  rapidly  as  it  is 
produced. 

COMMERCIAL   PRODUCTION   OF   OZONE   AND   ITS   APPLICATIONS. 

Among  the  early  plants  for  the  commercial  production  of  ozone 
for  its  practical  application  may  be  mentioned  two  equipments  in 
Germany,  where  ozone  is  used  as  a  sterilizing  and  oxidizing  agent 
in  connection  with  commercial  water-works  and  supplies.  These 
plants  are  situated  in  Schierstein,  near  Wiesbaden,  and  in  Paderborn 
respectively.  Ozone  is  well  adapted  for  water  sterilization  and 
purification,  being  a  powerful  destructive  agent  to  all  organic  matter 
both  animal  and  vegetable.  Of  its  efficiency  there  is  no  longer  any 
doubt,  as  experiments  conducted  over  a  long  space  of  time  all  go  to 
prove  its  great  efficiency.  The  question  lies  in  the  cost  entirely, 
and  in  order  to  secure  figures  of  value  upon  this  question  we  must 
study  a  commercial  working  equipment.  The  two  German  plants 
referred  to  were  installed  by  the  Siemens  &  Halske  Company,  of 
Berlin.  The  plant  at  Schierstein  is  designed  to  sterilize  66,000  gallons 
of  water  per  hour  as  a  maximum.  This  maximum  output  is  called 
for  only  on  occasions  when  exceptionally  large  quantities  of  water 
are  required,  while  the  average  demands  are  about  one-half  of  this, 
or  33,000  gallons  per  hour.  This  plant  is  divided  into  two  inde- 
pendent units,  like  lighting  and  power  units,  the  one  being  in  opera- 
tion while  the  other  is  at  rest.  The  electrical  generators  installed 
furnish  electricity  for  operating  pumps  for  the  air  and  water,  and 
also  for  working  the  step-up  transformers.  These  transformers 
receive  the  current  at  a  pressure  of  120  volts  and  supply  a  current 
from  the  secondary  winding,  at  a  pressure  of  8.000  volts,  the  second- 
aries of  course  being  connected  with  the  ozone-generators.  The 
ozone  produced  by  the  action  of  this  discharge  is  driven  by  fans  into 
the  sterilizing-towers,  in  which  the  ozone  rises  and  comes  in  contact 
with  the  water  flowing  down.  The  water  is  thus  intimately  mixed 
up  with  the  gas,  and  is  thereby  purified  and  flows  off  to  a  reservoir. 


PRODUCTION  OF  OZONE  AND   ITS   APPLICATIONS.  147 

In  the  ozonizer-room  there  are  48  ozone-generators  mounted  on 
stout  shelves  on  both  walls  opposite  an  aisle,  the  battery  being 
divided  into  two  halves  to  be  connected  with  the  two  generating 
units  respectively.  Each  half,  therefore,  contains  24  ozone  pro- 
ducers or  generators,  and  these  in  turn  are  divided  into  three  series, 
of  8  ozonizers  each,  and  each  series  of  eight  is  connected  to  the  8000- 
volt  secondary  winding  independently.  We  have,  therefore,  three 
sets  of  8  ozonizers  in  series,  connected  in  parallel  to  the  secondary 
of  the  transformer.  One  series  of  8  ozone-generators  produces  a 
sufficient  quantity  of  ozone  for  one  sterilization-tower.  The  ozon- 
izers are  of  the  Siemens-tube  type,  constructed  of  glass  and  metal, 
one  pole  being  grounded  on  account  of  the  method  employed  of 
cooling  the  inner  tube  with  water.  The  connections  to  the  positive 
pole,  the  pole  which  is  not  grounded,  are  well  protected,  so  that 
it  is  not  possible  for  the  attendants  to  meet  with  accidents  from  the 
high  potential.  Eight  ozonizing  tubes  or  generators  are  contained 
in  an  iron  box,  the  upper,  lower,  and  front  sides  of  which  are  provided 
with  heavy  glass  windows.  The  ozonizer-room  is  usually  kept 
darkened,  and  the  attendant  whose  duty  it  is  to  enter  it  sees  at  once 
from  the  blue  light  passing  through  the  glass  windows  of  the  ap- 
paratus whether  it  is  working  satisfactorily  or  not.  As  all  the  metallic 
parts  connected  to  the  8ooo-volt  poles  are  carefully  protected  on  the 
one  hand,  and  grounded  on  the  other,  there  is  little  danger  of  a  fatal 
accident.  The  sterilizing-room  in  this  plant  contains  two  series, 
each  of  four  towers,  of  brick.  Each  tower  is  divided  into  four 
sections  by  two  partition  walls  perpendicular  to  one  another.  These 
towers  are  filled  with  a  coarse  gravel  through  which  the  water  trickles 
on  its  downward  flow,  presenting  a  great  surface  to  the  action  of 
the  ascending  ozone.  Through  the  combined  four  sections  of  each 
tower,  11,100  gallons  of  water  are  flowing  downward  per  hour, 
while  in  the  same  time  2800  cubic  feet  of  ozonized  air  pass  upward 
through  the  gravel.  For  the  operation  of  each  half  of  the  plant, 
sterilizing  33,000  gallons  of  water  per  hour,  50  horse-power  are 
required,  of  which  27  horse-power  are  used  for  the  ozonizers,  22 
horse-power  for  the  pumps,  and  i  horse-power  for  various  minor 
purposes.  The  cost  of  the  process  at  Schierstein  is  0.35  cent  per 
cubic  meter  of  water  sterlized,  o.i  cent  being  the  cost  of  the  coal 
required  for  the  operation  of  the  ozonizing  apparatus.  To  this 


148  EXPERIMENTAL   ELECTROCHEMISTRY. 

must  of  course  be  added  the  usual  interest  on  the  money  invested 
in  the  plant,  and  the  cost  of  depreciation  and  repairs.  This  par- 
ticular plant  has  to  operate  pumps  in  addition  to  its  electrical  appara- 
tus, which  is  very  unusual,  and  can  be  deducted  from  the  cost  in 
almost  any  other  water-works.  Tests  of  the  sterilized  water,  made 
by  leading  German  chemists  and  bacteriologists,  proved  that  the 
sterilization  process  by  means  of  this  apparatus  is  in  every  way 
successful  so  far  as  the  annihilation  of  germs  and  bacteria  is  concerned. 
The  process  has  therefore  been  shown  to  be  well  adapted  to  the  purifi- 
cation of  drinking-water.  The  installation  at  Paderborn  is  similar 
to  that  at  Schierstein,  with  the  exception  of  the  sterilizing-towers. 
The  purified  water  in  this  plant  is  allowed  to  flow  off  in  the  form 
of  a  cascade,  in  order  that  the  contained  ozone  dissolved  may  be 
liberated  and  given  off.  The  cost  of  purifying  a  cubic  meter  of 
water  in  this  equipment  is  placed  at  0.4  cent,  including  interest, 
depreciation,  wages,  etc. 

Apparatus  has  been  designed,  and  constructed,  and  tested  at 
Niagara  Falls  in  this  country,  using  an  electrical  discharge  under 
a  potential  difference  of  50,000  volts  against  the  8000  employed  at 
the  German  works.  Ozone  produced  with  this  equipment  was 
passed  through  two  pipes  to  a  water-sterilizing-tower  partly  filled 
with  broken  rock,  one  supply-pipe  entering  the  bottom  and  the  other 
the  top  of  the  tower.  The  water  flowing  through  the  tower  down- 
ward meets  with  the  gas  from  all  sides,  above  and  below,  and  is 
purified  by  its  contact  with  the  several  ozone  streams.  It  is  claimed 
that  30  to  40  horse-power  are  sufficient  to  sterilize  6000  tons  of  water 
daily.  Some  interesting  experiments  have  been  conducted  by 
Warburg,  who  investigated  the  production  of  ozone  by  discharges 
in  a  closed  volume  of  oxygen.  In  this  case  the  formation  of  ozone 
has  a  limit  which  varies  widely  with  the  conditions  of  the  experiment. 
Besides  the  ozonizing  effect  of  the  electrical  discharges,  there  exists 
also  a  contrary  effect  which  counterbalances  the  production  after  at 
time.  Since  for  the  limited  duration  of  the  ozonizing  process  the 
spontaneous  decomposition  of  the  ozone  is  negligible,  it  follows  that 
the  electric  discharge  itself  must  produce  the  contrary  effect.  In 
endeavoring  to  obtain  a  measure  of  both  effects,  Warburg  starts 
from  the  assumption  that  the  ozonizing  effect  is  proportional  to  the 
number  of  molecules  of  oxygen  present,  while  the  decomposition 


PRODUCTION   OF   OZONE   AND    ITS   APPLICATIONS.          149 

is  proportional  to  the  number  of  ozone  molecules  present.  There 
is  a  decided  difference  between  the  behavior  of  a  positive  discharge 
and  that  of  a  negative  discharge;  the  maximum  percentage  of 
ozone  produced,  according  to  Warburg,  is  about  three  times  as  high 
for  negative  as  it  is  for  positive  discharges.  If  after  the  negative 
maximum  is  reached,  the  mixture  is  subjected  to  the  positive  dis- 
charge the  percentage  falls  to  the  positive  maximum.  The  de- 
composing activity  is  the  same  for  positive  and  negative  electricity, 
but  the  ozonizing  action  itself  is  three  times  higher  for  negative 
electricity.  The  effect  of  temperature  upon  both  discharges  is  the 
same.  The  author  has  not  verified  these  data,  but  introduces  them 
as  the  work  of  a  careful  and  reliable  experimenter.  If  partly  ozonized 
oxygen  is  left  to  itself,  the  proportion  of  ozone  decreases,  according 
to  Warburg,  in  an  interesting  manner  for  different  conditions.  This 
decrease  is  known  under  the  name  of  spontaneous  deozonization,  and 
may  be  due  to  a  great  variety  of  causes.  The  experimenter  referred 
to  points  out  that  since  the  amount  of  ozone  at  200°  C.  in  a  state 
of  equilibrium  is  inappreciable,  such  equilibrium  can  be  attained  at 
ordinary  temperatures  only  by  complete  dissociation  of  the  ozone. 
The  factors  bringing  about  this  dissociation  may  be  external,  as 
for  instance,  a  contact  with  foreign  bodies  or  with  the  walls  of  the 
vessel;  or  they  may  be  internal  and  due  to  the  collision  of  two 
molecules  of  ozone,  or  of  a  molecule  of  ozone  with  a  molecule  of 
oxygen.  Warburg  formulates  a  mathematical  theory  of  the  process^ 
and  finds  by  suitable  experiments  that  the  internal  effects  are  almost 
entirely  due  to  collisions  between  the  ozone  molecules  themselves.. 
Heat  increases  this  internal  disintegration  much  more  rapidly  than 
it  does  the  external  process,  and  it  becomes  the  chief  agent  at  high 
temperatures.  The  experimenter  in  question  finds  that  moisture 
makes  no  difference  in  the  stability  of  ozone  at  100°.  The  various, 
forms  of  ozone-generators  suggested  and  in  use  to-day  would  fill  a. 
volume  in  themselves,  and  it  is  believed  that  the  fundamental  prin- 
ciples and  typical  forms  introduced  here  will  be  a  sufficient  guide  to 
the  student  who  wishes  to  experiment  with  this  interesting  and 
valuable  modified  condition  of  oxygen.  In  the  next  chapter  another 
gaseous  product  will  be  dealt  with  of  no  less  scientific  interest  or 
technical  value.  This  will  pertain  to  the  electrical  production  of 
nitric  acid  from  the  atmosphere. 


CHAPTER  X. 

THE  PRODUCTION  OF  NITRIC  ACID  FROM  THE  ATMOSPHERE 
WITH  HISTORICAL  NOTES. 

WE  know,  as  general  chemists,  that  nitric  acid  is  one  of  the  most 
important  of  all  chemical  compounds,  and  that  it  is  usually  obtained 
from  potassium  nitrate,  which  is  obtained  as  an  incrustation  upon 
the  surface  of  the  soil  in  hot  and  dry  climates,  as  in  certain  parts  of 
India  and  Peru.  The  salt  imported  for  the  chemical  production  of 
nitric  acid  from  Bengal  and  Oude  consists  of  potassium  nitrate, 
while  the  Peruvian  or  Chilian  saltpeter  is  sodium  nitrate.  Either 
of  these  nitrates  serve  for  the  production  of  this  important  acid. 
On  a  small  scale  in  the  laboratory,  nitric  acid  is  prepared  by  the 
distillation  of  sodium  or  potassium  nitrate  with  an  equal  quantity 
by  weight  of  concentrated  sulphuric  acid.  The  decomposition  of 
potassium  nitrate  by  an  equal  weight  of  sulphuric  acid  is  represented 
by  the  following  chemical  equation: 

KNO3  +  H2SO4 =HNO3  +  KHSO4. 

It  would  appear  from  a  study  of  this  equation  that  one-half  of  the 
sulphuric  acid  might  be  saved,  inasmuch  as  one  molecule  could  be 
made  to  decompose  two  molecules  of  potassium  nitrate  as  follows: 

2KNO3  +  H2SO4  =  2HNO3  +  K2SO4, 

but  it  is  found  that  when  a  smaller  quantity  of  the  sulphuric  acid  is 
used  a  very  much  higher  temperature  is  necessary  to  bring  about  the 
complete  breaking  up  of  the  saltpeter,  and  that  much  of  the  nitric 
acid  is  decomposed,  and  the  normal  potassium  sulphate,  K2SO4, 
which  is  the  final  result,  is  much  more  troublesome  to  get  into  solu- 
tion in  order  to  remove  it  from  the  retort  or  still.  For  the  prepara- 
tion of  large  quantities  of  nitric  acid  sodium  nitrate  is  used  instead 

150 


NITRIC  ACID  FROM  THE  ATMOSPHERE.  151 

of  the  more  costly  potassium  nitrate.  The  chemical  production  of 
nitric  acid  dates  back  to  very  early  times.  Geber,  the  old  Arabian 
alchemist,  produced  this  acid  by  distilling  saltpeter,  copper  vitriol, 
and  alum.  As  early  as  the  thirteenth  century,  Raymund  Lullius 
described  its  preparation  by  distilling  saltpeter  with  iron  vitriol. 
Glauber,  in  the  seventeenth  century,  produced  it  by  the  same  method 
as  is  employed  to-day,  that  is  by  the  distillation  of  potassium  or 
sodium  nitrate  with  sulphuric  acid.  Cavendish,  in  his  studies  of 
the  atmosphere,  showed  that  it  consisted  of  a  mixture  of  oxygen  and 
nitrogen.  Although  these  elements  in  their  pure  condition  show 
no  attraction  for  each  other,  five  distinct  compounds  of  oxygen  and 
nitrogen  are  prepared  in  various  indirect  ways.  These  compounds, 
which  should  be  familiar  to  all  of  us  who  have  given  attention  to 
general  inorganic  chemistry,  are  as  follows: 

N2O,    nitrous  oxide; 
NO,     nitric  oxide; 
N2Os,  nitrogen  trioxide ; 
NO 2,   nitrogen  peroxide; 
N2O5,  nitrogen  pentoxide. 

When  a  succession  of  powerful  electric  sparks  were  made  to  pass 
through  dry  air  in  a  flask,  a  red  gas,  NO2,  nitrogen  peroxide,  was 
formed,  and  when  these  discharges  were  allowed  to  take  place  in  the 
presence  of  moisture,  this  gas  was  absorbed  and  converted  into  a 
mixture  of  nitrous  and  nitric  acids, 


If  instead  of  water  we  place  in  the  flask  a  weak  solution  of  potassium 
hydroxide,  instead  of  obtaining  the  mixed  acids,  we  obtain  the  two 
salts,  potassium  nitrite,  and  potassium  nitrate: 


HNO2  +  KOH=KNO2 
HNO3  +  KOH  =  KNO3  +  H2O. 

By  evaporating  to  dryness  such  a  solution,  we  obtain  a  saltpeter 
consisting  of  potassium  nitrite  and  potassium  nitrate,  and  if  we 
distill  this  product  with  strong  sulphuric  acid  we  will  obtain  nitric 
acid.  Cavendish  went  through  this  process  and  prepared  the  above 


EXPERIMENTAL   ELECTROCHEMISTRY. 


compounds  without  difficulty.  If  the  experiment  of  passing  sparks 
through  air  (for  best  effects  the  air  should  be  mixed  with  some  pure 
oxygen)  be  repeated  in  a  U  tube  having  one  of  the  vertical  limbs 
of  the  tube  provided  with  a  stoppered  globe  into  which  the  two 
sparking  wires  are  sealed,  and  we  fill  this  system,  all  but  the  globe, 
with  water  colored  blue  with  litmus,  the  solution  will  be  reddened 
by  the  acids  formed,  and  the  air  in  the  globe  will  be  found  to  diminish 
in  volume.  Fig.  73  shows  this  form  of  "U  "  tube  and  the  arrange- 


FIG.  73. — Special  Form  of  U  Tube  for  Showing  Absorption  of  the  Oxides  of  Nitrogen. 

by  Water. 

ment  of  the  experiment.  The  blue  litmus  solution  is  placed  in  the 
tube  with  the -stopper  in  place  so  that  we  will  have  a  difference  in  levels 
as  indicated  in  the  illustration.  A  little  scale,  as  shown  at  the  left, 
assists  us  in  determining  the  diminution  in  volume  when  the  oxides 
of  nitrogen  combine  with  the  contained  water.  This  formation  of 
oxides  of  nitrogen  may  be  regarded  as  the  combustion  of  nitrogen  in 
oxygen  due  to  the  kindling  effect  of  the  electric  spark.  A  simple  non- 
electrical experiment  to  illustrate  the  probable  combustion  of  nitrogen 
in  oxygen  may  be  performed  by  igniting  a  piece  of  magnesium  ribbon 
in  a  tall  glass  jar  of  carefully  dried  air.  If  such  an  experiment  be 
performed  and  one  looks  down  into  the  jar  red  fumes  may  be  seen 
and  the  presence  of  oxides  of  nitrogen  may  be  shown  by  drawing  the 
contents  of  the  jar  through  a  mixture  of  potassium  iodide  with  starch 
and  acetic  acid,  when  the  iodine  will  be  set  free,  which  blues  the 


NITRIC   ACID  FROM  THE  ATMOSPHERE.  153 

starch.  This  experiment  makes  it  appear  likely  that  the  electric 
spark  causes  the  combustion  of  nitrogen  in  oxygen  on  account  of  a 
kindling  effect.  When  ozonized  air  is  passed  into  water  nitric  acid 
is  found  in  solution.  It  has  also  been  shown  that  rain-water  contains 
about  one  part  per  million  of  nitric  acid.  When  hydrogen  gas, 
mixed  with  a  small  quantity  of  nitrogen,  is  burned,  the  water  collected 
as  the  result  of  the  combustion  is  found  to  be  slightly  acid,  due  to  the 
presence  of  some  nitric  acid,  due  to  the  combination  of  the  nitrogen 
with  the  oxygen  of  the  air  under  the  high  temperature  of  the  burning 
hydrogen.  With  the  recording  and  appreciation  of  such  experiments 
a  new  method  of  preparing  nitric  acid  began  to  dawn  upon  chemists 
in  general.  In  the  year  1859,  Newton  produced  nitric  acid  from 
the  atmosphere  by  constructing  a  modified  form  of  U  tube  and 
bulb,  differing  from  that  already  illustrated  only  in  the  shape  of  the 
chamber.  Newton  employed  a  more  spacious  design  of  chamber 
for  the  air  and  water  into  which  he  inserted  his  sparking  wires. 
Means  were  provided  in  this  chamber  for  sending  in  a  fresh  supply 
of  air  and  for  allowing  the  acidulated  water  produced  to  run  off. 
Prim,  in  1882,  modified  this  arrangement  and  used  both  a  silent 
electrical  discharge  and  a  series  of  sparks  to  bring  about  the  combina- 
tion of  the  nitrogen  with  the  oxygen  present  in  a  chamber.  In  the 
year  1^92  Sir  William  Crooks  produced  what  he  termed  an  electric 
flame,  through  the  agency  of  a  high  voltage  alternating  electric  cur- 
rent discharge  between  pieces  of  platinum,  and  by  its  means  brought 
about  the  combustion  of  nitrogen  in  oxygen.  Lord  Rayleigh  and 
Professor  Ramsay  employed  such  a  flaming  arc  in  a  number  of  their 
researches  upon  the  atmosphere  in  connection  with  the  oxidation  of 
nitrogen.  They  employed  an  alternating  current  stepped  up  to  a 
difference  of  potential  of  8000  volts.  Lord  Rayleigh  in  his  work  upon 
the  production  of  nitric  acid  from  the  atmosphere  employed  a  spherical 
glass  chamber  with  a  capacity  of  about  50  liters  in  which  could  be 
maintained  a  fountain  of  sodium  or  potassium  hydroxide  solution. 
Into  this  chamber  air  and  oxygen  were  slowly  pumped  containing 
a  flaming  discharge  between  platinum  terminals.  It  is  stated  that 
Lord  Rayleigh  produced  with  this  equipment  about  40  grams  of 
nitric  acid  per  hour  with  the  expenditure  of  about  one  electrical 
horse-power  in  energy.  McDougall  and  Howies  describe  an  equip- 
ment for  producing  nitric  acid  from  the  atmosphere,  and  its  per- 


154  EXPERIMENTAL   ELECTROCHEMISTRY. 

formance,  which  is  of  special  interest  to  the  student  in  this  line  of 
work.  They  outline  an  alternating  current-generator  with  a  fre- 
quency of  60,  equipped  with  two  separate  armature  circuits.  One 
of  these  windings  delivers  a  current  of  24  amperes  at  200  volts 
pressure,  and  the  other  12  amperes  at  400  volts  pressure.  The 
current  of  this  alternator,  from  either  winding  at  will,  can  be  led  to 


FIG.  74. — Stone. ware  Pipe  used  as  Combustion  Chamber  for  Producing  Nitric  Acid 

from  Atmosphere. 

a  step-up  transformer  with  a  ratio  of  i  to  40,  so  it  will  be  seen  that 
a  voltage  at  the  secondary  winding  of  the  transformer  of  either 
8000  or  16,000  volts  may  be  obtained.  The  current  in  the  primary 
of  the  transformer  may  be  very  closely  measured  by  inserting  an 
ammeter,  and  through  the  agency  of  a  voltmeter  at  the  terminal  of 
the  alternator  the  initial  electrical  pressure  can  be  recorded.  A 


NITRIC   ACID  FROM  THE  ATMOSPHERE. 


'55 


wattmeter  was  also  included  in  the  primary  circuit  by  means  of 
which  the  readings  of  the  voltmeter  and  the  ammeter  could  be  checked 
and  the  energy  consumed  in  the  flaming  discharge  could  be  ascer- 
tained. An  early  form  of  combustion  chamber  equipped  with 
platinum-iridium  electrodes  for  the  production  of  nitric  acid  from 
the  atmosphere  with  this  electrical  equipment,  consisted  of  a  stone- 
ware pipe  of  the  shape  depicted  in  Fig.  74.  Air  is  drawn  through 
this  chamber  during  the  time  of  an  electrical  discharge,  and  the 
oxidized  nitrogen  is  drawn  through  a  series  of  Woulf  bottles  con- 
taining either  water,  or  a  solution  of  sodium  hydroxide.  Instead 
of  employing  the  Woulf  bottles  a  series  of  towers  may  be  employed 
to  great  advantage,  each  tower  containing  broken  glass  for  the 


FIG.  75. — Modified  Form  of  Combustion  Chamber  for  the  Production  of  Nitric  Acid. 

water  to  run  over  and  cause  it  to  present  a  great  surface  for  absorp- 
tion to  the  oxides  of  nitrogen  which  are  made  to  pass  through.  We 
can  produce  a  solution  of  sodium  nitrate,  or  free  acid,  at  will  with 
this  equipment.  The  form  of  the  combustion  chamber  itself  under- 
went numerous  evolutions,  one  or  two  of  the  shapes  being  given  here 
as  a  matter  of  interest  and  guide  to  the  student.  Fig.  75  shows  one 


156 


EXPERIMENTAL   ELECTROCHEMISTRY. 


of  these  modifications.  This  chamber  consists  of  a  large  stoneware 
bottle  with  vertical  supply  and  outlet  tubes  for  the  gases.  Lord 
Rayleigh  showed  that  these  combustion  chambers  should  be  quite 
spacious ;  in  other  words,  that  there  should  be  a  considerable  amount 
of  room  about  the  flaming  discharge.  If  the  air  is  not  passed  through 
at  a  certain  maximum  rate,  the  oxides  of  nitrogen  formed  will  be 
broken  up  again  by  the  discharge,  very  much  like  the  behavior  of 
ozone  when  subjected  to  heat  after  its  formation.  The  oxides  of 
nitrogen  should  be  removed  from  the  field,  or  influence  of  the  arc  as 
soon  as  possible  for  high  efficiency  in  yield.  A  too  rapid  supply  of 
air  causes  the  electrical  discharge  to  become  unsteady,  and  a  loss  in 
efficiency  results.  Some  interesting  and  valuable  data  were  obtained 
on  nitric  acid  from  air  by  McDougall  and  Howies  using  various 
forms  of  combustion  chambers,  and  supplying  the  electricity  under 
different  conditions.  Fig.  76  is  another  form  of  combustion  chamber 


FIG.  76. — Another  Modification  of  Combustion  Chamber. 

as  described  in  the  work  of  these  experimenters.  They  varied  the 
forms  and  sizes  of  the  chambers,  keeping  the  electrical  conditions 
constant,  and  kept  the  forms  of  combustion  chambers  constant, 


NITRIC    ACID  FROM  THE  ATMOSPHERE.  157 

and  varied  the  character  of  the  electrical  discharges,  making  quanti- 
tative determinations  of  the  nitric  acid  obtained  in  each  case.  By 
varying  the  current  value  in  the  secondary  circuit  of  the  transformer, 
keeping  the  voltage  constant,  these  experimenters  were  able  to  vary 
the  temperature  of  the  flaming  discharge,  and  to  study  its  effect  upon 
the  yield  of  nitric  acid  produced.  They  formulated  the  following 
table  which  brings  out  the  fact  that  a  high  temperature  discharge  is 
unfavorable  to  high  efficiency,  and  consequently  we  can  produce 
more  acid  with  a  fewer  number  of  watts,  or,  in  other  words,  with  less 
electrical  horse-power. 

Watts  Used  Current  Used  in  Yield  of  Acid  per  H.P. 

in  Flame.  Flame.  per  12  Houvs. 

302  -3  to  .38  ampere  180  grams 

225  .2    "     .25  "  270         " 

172  .15   "       .2          "  300         " 

Too  great  a  decrease  in  the  current  value  of  the  flame  caused  the 
flaming  arc  to  become t  unsteady  and  liable  to  extinction.  The 
production  of  nitric  acid  by  these  experimenters  with  the  foregoing 
electrical  equipment  and  design  of  chambers,  at  the  rate  of  300 
grams  of  nitric  acid  per  horse-power  for  twelve  hours,  represents 
51.5  per  cent  of  the  amount  theoretically  obtainable  from  the  amount 
of  air  supplied.  This  result  compares  very  favorably  with  the 
figures  obtained  by  Lord  Rayleigh,  working  with  a  mixture  of  oxy- 
gen and  nitrogen  in  the  proportion  of  two  volumes  of  oxygen  to  one 
volume  of  nitrogen,  when  he  obtained  440  grams  of  nitric  acid 
in  the  same  time  and  with  the  same  consumption  of  electrical  energy. 
When  ordinary  air  is  used  in  these  chambers,  the  theoretical  pro- 
portions of  oxygen  and  nitrogen  for  the  production  of  the  oxide 
are  diluted  with  an  excess  of  nitrogen,  which  of  course  is  detrimental 
to  the  best  effects.  An  experiment  was  conducted  in  one  of  these 
chambers  with  a  mixture  of  pure  oxygen  and  nitrogen  gases  in  the 
proportion  of  one  volume  of  oxygen  to  two  volumes  of  nitrogen,  and 
the  yield  was  590  grams  of  acid.  To  study  the  effects  of  tem- 
perature upon  the  rate  of  oxidation,  the  air  supplied  to  the  com- 
bustion chamber  was  raised  in  temperature  by  passing  it  through 
a  porcelain  tube  packed  with  asbestos,  around  which  a  heating 
coil  of  platinum  wire  was  wound.  On  passing  a  strong  current 
of  electricity  through  this  wire  in  the  tube,  the  entire  system  was 


158  EXPERIMENTAL   ELECTROCHEMISTRY. 

elevated  in  temperature  to  incandescence,  and  the  air  after  passing 
through  was  immediately  treated  in  the  flaming  discharge.  This 
porcelain  tube  was  cemented  directly  into  the  stoneware  combus- 
tion chamber.  A  marked  decrease  in  the  yield  of  nitric  acid  was 
noted  with  the  same  supply  of  energy.  This  behavior  is  entirely 
in  accord  with  the  behavior  of  air  when  treated  to  form  ozone. 
Kowalski  describes  his  apparatus  and  method  for  producing  nitric 
acid  from  the  atmosphere,  and  states  that  the  yield  of  product  is 
largely  dependent  upon  the  frequency  of  the  alternating  current 
used  for  the  flaming  discharge.  At  high  frequencies  the  best  re- 
sults are  attained.  Kowalski  and  Moscicki,  working  with  an 
alternating  current  with  a  frequency  between  5000  and  6000  cycles 
per  second,  obtained  43.5  grams  of  nitric  acid  per  kilowatt  hour 
with  an  amperage  in  the  secondary  of  .2.  They  have  also  con- 
firmed the  work  of  McDougall  and  Howies  and  others,  that  the 
amperage  in  the  secondary  of  the  transformer  has  a  direct  bearing 
upon  the  yield,  and  that  for  high  current  strength  the  yields  of  acid 
are  not  so  great.  The  present  writer  has  also  fully  confirmed  this 
statement.  Kowalski  and  Moscicki  also  found  that  the  influence 
of  the  length  of  the  flaming  discharge  is  decided.  With  a  current 
in  the  secondary  of  only  .05  ampere  and  a  difference  of  potential  of 
50,000  volts,  and  a  frequency  of  6000  to  10,000  cycles  per  second, 
they  obtained  a  maximum  yield  of  nitrous  vapors  for  the  energy 
employed.  They  have  obtained  from  52  to  55  grams  of  nitric  acid 
per  kilowatt  hour,  which  yield  could  be  nearly  doubled  by  adding 
about  50  per  cent  of  pure  oxygen  gas  to  the  air  employed  in'  the 
combustion  chamber.  The  work  of  Bradley  and  Lovejoy  for  the 
production  of  nitric  acid  from  the  atmosphere  upon  a  large  scale  is 
especially  noteworthy.  They  point  out  that  whereas  the  silent 
electrical  discharge,  and  the  spark  or  disruptive  discharge  can 
cause  the  combination  of  oxygen  and  nitrogen  gases,  they  have  but 
feeble  capacity  in  point  of  efficiency,  which  is  also  the  case  with  the 
ordinary  arc.  To  obtain  the  best  results  they  point  out,  as  a  result 
of  lengthy  researches,  that  it  is  necessary  to  employ  an  arc  divided 
into  numerous  thin  and  flat  subdivisions  in  order  to  present  a  large 
surface  for  a  small  amount  of  electrical  energy.  This  work  is  only 
in  keeping  with  that  of  previous  experimenters.  They  point  out  that 
the  thinner  the  arc  the  greater  the  efficiency  of  the  process  up  to 


NITRIC   ACID  FROM  THE  ATMOSPHERE.  i$9 

the  point  where  the  arc  breaks.  It  is  necessary  for  best  effects  to 
greatly  subdivide  the  current  by  arranging  the  arc  circuits  in  par- 
allel. In  the  experimental  apparatus  of  Bradley  and  Love  joy,  they 
employ  a  direct  current  of  .75  ampere  at  a  pressure  of  8000  volts, 
which  can  be  increased  to  several  ampers  at  15,000  volts.  There 
are  138  arcs  between  which  this  current  is  divided,  each  of  which 
is  made  and  broken  by  a  revolving  mechanism  50  times  per  second. 
Each  arc  has  a  current  value  of  only  .005  ampere.  The  arcs  are 
all  produced  successively,  and  not  at  one  time,  by  a  special  arrange- 
ment of  the  wire  electrodes  on  the  revolving  drum  which  carries  them. 
In  their  recent  apparatus  there  are  6900  arcs  formed  and  extinguished 
per  second,  each  arc  lasting  only  for  the  brief  period  of  1/20,000  of 
a  second.  As  each  little  arc  tends  to  increase  in  volume,  due  to 
increased  conductivity  as  soon  as  it  is  formed,  the  tendency  to  short 
circuit  the  others  is  avoided  by  placing  inductance-coils  in  series 
with  the  arcs.  These  small  inductance-coils  are  so  designed  and 
calculated  that  during  about  1/40,000  of  a  second  they  delay  or  im- 
pede the  flow  of  the  current,  thereby  preventing  a  rapid  growth 
of  the  arc,  and  during  the  succeeding  1/40,000  of  a  second,  while  the 
arc  is  being  drawn  out  by  the  revolving-drum  carrier,  it  sends  an  im- 
pulse which  increases  the  current  flow  and  so  prolongs  the  arc. 
With  a  difference  of  potential  of  8000,  and  about  1/200  of  an  ampere 
of  current,  the  arcs  are  drawn  out  4  to  6  inches,  and  the  oxygen  and 
nitrogen  treated  to  this  discharge.  As  in  the  production  of  ozone, 
the  molecules  of  nitrogen  oxide  must  be  removed  from  the  field  before 
the  atoms  of  oxygen  and  nitrogen  dissociate,  and  this  point  is 
especially  remarked  upon  by  these  later  investigators.  The  appara- 
tus installed  at  Niagara  Falls  by  Bradley  and  Lovejoy  is  about 
5  feet  high  by  4  feet  in  diameter,  built  of  iron  of  cylindrical  form. 
Six  rows  of  inlet  wires,  well  insulated  by  porcelain  sleeves,  enter  the 
sides  of  this  chamber.  The  terminals  of  the  electrodes  are  of  plati- 
num wire,  turned  downwards  to  spread  out  the  arc  in  a  thin  flat 
discharge.  In  the  center  of  the  iron  cylinder  is  a  shaft  vertically 
arranged,  carrying  a  series  of  23  radial  arms,  corresponding  to  the 
23  rows  of  points  which  enter  the  sides,  there  being  six  radial  arms 
in  each  plane.  These  radial  arms  are  each  tipped  with  platinum 
wire,  which  come  within  1/25  of  an  inch  of  the  platinum  wires  of  the 
opposite  stationary  poles.  As  the  two  platinum  wire  points  approach 


160  EXPERIMENTAL    ELECTROCHEMISTRY. 

upon  the  turning  of  the  shaft,  a  spark  jumps  a  gap  of  about  J  of 
an  inch  to  meet  the  approaching  platinum  point,  and  then  the  arc  is 
drawn  out  from  4  to  6  inches  by  the  retreating  point  until  it  breaks. 
If  it  were  not  for  the  little  inductance-coils  in  series  with  these  arcs, 
it  is  evident  that  we  would  have  a  comparatively  heavy  arc  at  the 
time  of  formation,  increasing  as  the  points  come  nearer  together. 
Each  of  these  coils  is  immersed  in  oil,  and  is  5  inches  in  diameter 
by  12  inches  long,  and  contains  several  thousand  turns  of  fine  in- 
sulated wire.  The  central  shaft  carrying  the  moving  electrode 
points,  is  turned  at  the  rate  of  500  revolutions  per  minute,  and 
takes  a  little  over  i  horse-power.  The  efficiency  of  this  piece 
of  apparatus  is  stated  to  be  i  pound  of  nitric  acid,  per  7  elec- 
trical horse-power  per  hour.  Carefully  dried  air  is  used  in  this 
combustion  chamber,  which  is  protected  by  a  coating  on  the  inside 
of  asphalt  varnish.  If  moisture  was  present  in  the  air,  nitric  acid 
would  be  formed  within  the  chamber,  and  would  in  time  lead  to 
serious  corrosions.  The  oxides  of  nitrogen  are  led  to  a  tower  down 
and  through  which  water  trickles,  for  the  production  of  nitric  acid, 
or  a  solution  of  sodium  hydroxide,  for  the  production  of  sodium 
nitrate.  It  has  been  suggested  that  milk  of  lime  be  made  to  flow 
through  one  of  these  towers  for  the  production  of  calcium  nitrate 
for  fertilizing  purposes.  This  is  reported  to  be  a  cheaper  method 
of  getting  nitrogen  into  the  soil  than  by  using  sodium  nitrate,  with 
lime,  at  $1.50  per  ton.  The  present  writer  has  experimented  with 
both  ozone  production  and  nitric-acid  production,  employing  volt- 
ages as  high  as  250,000,  and  is  able  to  confirm  the  results  of  these 
experimenters  from  his  own  note-book.  This  field  is  one  of  great 
charm  to  the  student  of  electrochemistry,  and  a  few  concise  details 
as  to  methods  of  producing  nitric  acid  from  the  air  may  prove 
welcome  to  him.  Although  the  foregoing  work  by  others  in  this 
line  will  give  the  student  the  fundamental  principles  involved,  and 
the  basic  information  upon  which  to  experiment,  a  few  specific 
directions  may  not  be  out  of  order.  Let  us  construct  ourselves 
a  simple  piece  of  apparatus  of  our  own  design  for  producing  nitric 
acid  by  electrical  means  for  use  in  the  laboratory  or  lecture-room. 
Fig.  77  shows  a  simple  and  easily  constructed  design  of  chamber 
for  rotating  electrodes,  and  which  has  proven  most  satisfactory  in 
the  laboratories  of  The  George  Washington  University,  where  it 


NITRIC   ACID  FROM  THE  ATMOSPHERE. 


161 


was   built   and   operated.     This   chamber  consists   of  a   casing  of 
pine  wood  with  an  outside  diameter  of  14  inches,  and  an  internal 


, 


diameter  of  nj  inches.     The  internal  width  of  the  chamber  is  3 
inches.     The  shell  for  this  chamber  was  cut  out  on  a  band-saw  at 


162  EXPERIMENTAL   ELECTROCHEMISTRY. 

a  lumber  mill,  and  two  wooden  side  plates  securely  screwed  against 
the  sides.  The  chamber  was  carefully  protected  on  the  inside  by 
several  coats  of  acid-proof  paint.  The  steel  spindle  which  carries 
the  hub  into  which  the  four  electrodes  are  screwed,  is  supported,  and 
turns  into  holes  drilled  in  two  disks  of  hard  rubber,  screwed  against 
the  sides  of  the  casing.  The  wood  of  the  casing  is  cut  away  at  the 
center  so  the  steel  spindle  constituting  one  pole  of  the  high-tension 
alternating  current  is  in  contact  with  hard  rubber  only.  These 
circular  openings  in  the  wood  are  6  inches  in  diameter,  and  the 
diameter  of  the  hard-rubber  plates  screwed  against  the  sides  is 
8J  inches.  The  stationary  electrode  which  protrudes  through 
the  top  in  a  vertical  position  is  connected  to  the  other  terminal  of 
the  high  potential  transformer,  and  is  carefully  insulated  from  the 
wooden  casing  by  passing  through  a  hard -rubber  tube.  There  is 
a  brass  commutator  wheel  on  the  outside,  as  shown,  upon  which  a 
brass  brush  rests,  which  is  in  turn  supported  by  a  hard-rubber  block, 
as  shown.  A  hard-rubber  grooved  pulley  is  on  the  end- of  the  shaft 
for  the  belt  of  the  driving  motor.  On  no  account  construct  this 
apparatus  without  the  generous  use  of  hard  rubber,  for  in  our  ex- 
perimental work  it  may  be  desirable  to  increase  the  voltage  to  16,000 
or  to  even  32,000,  and  ordinary  wooden  insulation  would  be  value- 
less as  an  effective  insulator.  An  inlet  and  outlet  tube  must  be 
provided,  as  shown,  for  the  air-supply,  and  a  little  glass  window 
should  be  provided  to  enable  us  to  see  the  condition  of  the  electrical 
flame  within.  Fig.  78  shows  this  piece  of  apparatus  assembled  in 
connection  with  a  transformer  for  high  potential  electrical  discharges, 
a  driving  motor  for  the  electrodes,  a  foot-bellows  for  air-supply,  and 
a  Woulf  bottle  for  the  absorption  of  the  oxides  of  nitrogen  in 
either  water  or  caustic  soda.  The  mechanical  and  electrical  con- 
ditions set  down  in  one  experiment  with  the  present  equipment 
are  as  follows: 

Revolutions  per  minute  of  electrodes 150 

Alternating  current  cycles  per  second 60 

Complete  reversals,  therefore,  per  second 120 

Voltage  at  secondary  of  transformer 10,000 

Amperage  in  flaming  arc 1/25 

Jump  gap  when  electrodes  were  opposite  each 

other  in  fraction  of  an  inch 1/16 

Length  of  flaming  arc  at  time  of  breaking  by 

being  drawn  out,  in  inches 3^ 

Appearance  of  flaming  arc Pale  yellow 

Type  of  transformer Oil  immersion 


NITRIC   ACID  FROM  THE  ATMOSPHERE. 


163 


With  these  conditions  the  yield  of  nitric  acid  was  excellent,  taking 
in  the  air  at  the  temperature  of  the  laboratory.     This  apparatus. 


was  operated  under  various  conditions  and  the  oxides  of  nitrogen- 
estimated  in  several  ways.     In  the  place  of   the   Woulf    bottle,   IT 


1 64  EXPERIMENTAL  ELECTROCHEMISTRY. 

tubes  were  substituted  in  several  runs,  which  were  immersed  in  large 
beakers  of  liquid  air,  when  the  oxides  of  nitrogen  were  condensed 
to  a  light-blue  solid  and  estimated  in  this  form.  It  is  believed  that 
the  construction  and  operation  of  this  piece  of  apparatus  will  fully 
repay  the  student  having  at  hand  the  necessary  high  potential 
electrical  discharge  for  the  production  of  nitric  acid. 


CHAPTER  XI. 
THE   ISOLATION   OF  THE  METALS   SODIUM   AND   POTASSIUM. 

BY  giving  specific  attention  to  the  metal  sodium  in  this  chapter 
we  will  also  be  covering  in  a  general  manner  the  means  employed 
for  the  isolation  of  potassium.  We  will,  therefore,  refer  to  sodium. 
in  this  chapter,  and  it  will  be  understood  that  potassium  may  also  be 
isolated  by  similar  apparatus  introduced  and  used  under  like  con- 
ditions. Sodium  is  much  cheaper  than  potassium,  as  it  is  well 
known  by  all  chemists,  because  of  the  greater  abundance  of  cheap 
sodium  salts.  As  we  learned  in  the  opening  chapter  Sir  Humphry 
Davy  was  the  first  to  obtain  metallic  sodium  through  the  agency  of 
the  electric  current  and  a  mercury  cathode.  We  know  that  sodium 
is  one  of  the  most  abundant  of  all  chemical  elements,  and  that  it  occurs 
in  immense  quantities  in  combination  as  rock-salt  deposits  in  saline 
springs  and  in  sea-water.  Sodium  also  occurs  in  the  form  of 
nitrates,  borates,  carbonates,  etc.,  etc. 

The  cheapest  source  of  sodium  is,  of  course,  from  sodium  chloride 
or  common  salt.  Rock  salt  forms  very  considerable  deposits  in 
many  regions.  Among  the  most  important  are  those  at  Northwich, 
in  Cheshire,  England,  where  very  large  quantities  are  extracted  by 
mining  processes. 

Sodium  has  been  prepared  by  an  ordinary  chemical  process  by 
reducing  its  oxide  by  carbon  at  a  white  heat.  The  following  chemical 
equation  indicates  the  character  of  the  reaction: 


This  old  process  was  worked  by  taking  30  kilograms  of  dry 
sodium  carbonate,  13  kilograms  of  charcoal,  and  3  kilograms  of 
chalk.  These  were  thoroughly  mixed  together,  calcined,  and  intro- 
duced into  iron  cylinders  heated  in  reverberatory  furnaces.  At 

165 


1 66  EXPERIMENTAL   ELECTROCHEMISTRY. 

a  bright  red  heat  the  sodium  distills  over  and  is  collected  in  suitable 
receivers.  It  is  purified  by  redistillation,  and  then  melted  under 
petroleum  into  ingots  which  are  preserved  under  naphtha  or  other 
suitable  hydrocarbon. 

Another  chemical  process  devised  by  Castner,  consisted  in  reducing 
sodium  hydroxide  by  heating  it  to  a  temperature  of  850°  C.  with  an 
intimate  mixture  of  finely  divided  iron  and  carbon  prepared  by 
mixing  the  iron  with  molten  pitch.  These  old  chemical  methods 
Lave  been  entirely  replaced  by  electrolytic  processes,  and  it  is  the 
purpose  of  this  chapter  to  outline  the  principle  upon  which  the 
electrochemical  method  is  dependent.  As  we  have  learned,  the 
electrolytic  decomposition  of  sodium  and  potassium  hydroxides  led 
to  the  discovery  of  these  metals.  Sir  Humphry  Davy,  writing  in  the 
Philosophical  Transaction  in  1810,  describes  his  research  as  follows: 

"By  means  of  a  stream  of  oxygen  gas  from  a  gasometer  applied 
to  the  flame  of  a  spirit-lamp,  which  was  thrown  on  a  platina  spoon 
containing  potash,  this  alkali  was  kept  for  some  minutes  in  a  strong 
red  heat,  and  in  a  state  of  perfect  fluidity.  The  spoon  was  preserved 
in  communication  with  the  positive  of  the  battery  of  the  power  of 
100  of  6  inches,  highly  charged,  and  the  connection  from  the  negative 
side  was  made  by  a  platina  wire." 

This  method  of  Sir  Humphry  Davy,  although  theoretically 
attractive,  does  not  work  very  smoothly  in  practice  and  we  will  see 
that  very  special  precautions  must  be  taken  in  order  to  get  a  satis- 
factory yield  of  either  metallic  sodium  or  potassium.  Many  modifi- 
cations of  this  classic  experiment  have  been  made,  among  which 
may  be  mentioned  the  use  of  a  platinum  dish  containing  a  strong 
solution  of  potassium  hydroxide  and  metallic  mercury  in  the  bottom, 
which  is  connected  to  the  negative  electrode  of  a  suitable  battery. 
We  have  here  the  dawn  of  the  practical  processes  which  followed 
where  the  containing  vessel  is  made  the  cathode  in  electrolysis. 
One  of  the  earliest  designs  of  commercial  apparatus  is  that  of  Charles 
Watt,  which  is  described, in  his  specifications  in  1851.  The  following 
account  is  from  his  own  specifications:  "The  second  part  of  my 
invention  consists  of  a  mode  of  preparing  or  obtaining  the  metals  of 
the  alkalies  and  alkaline  earths  by  the  united  action  of  electricity 
and  heat.  For  performing  this  part  of  my  invention  by  the  united 
action  of  electricity  and  heat,  I  employ  a  vessel  [of  the  form  shown 


THE  ISOLATION   OF  THE   METALS   SODIUM   AND   POTASSIUM.    167 

in  Fig.  79],  which  is  made  of  iron  or  other  suitable  material  capable 
of  bearing  a  full  red  heat.  In  this  figure  A  is  the  vessel,  which 
should  be  at  least  one-half  an  inch  thick,  and,  if  made  of  iron,  previ- 
ously to  its  being  used  should  be  coated  over  its  exterior  with  clay 
or  other  substance  to  preserve  it  from  the  action  of  the  fire;  B, 
movable  head  for  the  collection  of  the  metals;  C,  electrodes,  with 


B 


FIG.  79. — Watt's  Electrolytic  Cell  for  the  Production  of  Sodium  and  Potassium. 


their  attachments  E;  D,  flanges  to  support  the  vessel  upon  the  furnace. 
The  covered  compartment  F,  being  that  in  which  it  is  intended  to 
eliminate  the  metals,  is  supplied  with  a  carbon  electrode  and  the 
uncovered  compartment  is  supplied  with  a  gold  electrode;  but  I 
wish  it  to  be  understood  that  I  do  not  restrict  myself  to  the  particular 
form  of  apparatus,  or  to  the  material  to  be  used  for  electrodes.  The 
vessel  is  filled  with  dry  saline  matter,  so  that  when  it  is  in  a  state  of 
fusion  it  shall  reach  the  dotted  lines  [the  author  has  shown  a  full 
black  line  drawn  across  the  interior  of  the  cell];  the  partition  keeps 
the  eliminated  substances  from  reacting  on  each  other,  and  also 


1 68  EXPERIMENTAL   ELECTROCHEMISTRY. 

excludes  air  from  the  compartment  in  which  the  metal  is  eliminated, 
the  access  of  which  would  cause  the  metal  to  be  oxidized.  The 
vessel  is  placed  in  a  furnace  where  it  can  be  subjected  to  the  action 
of  a  full  red  heat,  and  when  the  saline  matter  is  in  a  state  of  fusion 
contact  is  made  between  the  decomposing  vessel  and  the  apparatus 
supplying  the  electric  current  or  currents,  the  intensity  of  which 
should,  at  least,  be  equal  to  that  which  would  be  supplied  by  10  cells 
of  DanielFs  battery  arranged  for  intensity,  but,  of  course,  this  depends 
upon  the  nature  of  the  salt  which  is  being  decomposed.  The  fused 
salt  is  maintained  at  that  temperature  which  will  ensure  the  instantane- 
ous volatilization  of  the  metal  as  it  is  eliminated,  and  a  proper  receiver 
(such  a  one  as  is  usually  employed  for  the  preparation  of  such  metals 
will  answer)  is  connected  air-tight  with  the  narrow  tube  projecting 
from  the  head.  The  metal  is  received  and  preserved  in  any  con- 
venient fluid  hydrocarbon.  The  salts  which  I  usually  employ  are  the 
chlorides,  iodides,  or  bromides  of  the  metals  of  the  alkalies  or  alka- 
line earths." 

This  historic  piece  of  apparatus  proved  to  be  absolutely  worthless 
in  commercial  practice,  for  it  is  impossible  to  successfully  distill  such 
metals  in  a  retort  chamber  of  this  peculiar  design.  There  are 
many  weak  features  about  this  apparatus  which  condemn  it  for  all 
serious  uses.  The  gold  anode,  apart  from  its  prohibitive  cost,  would 
have  but  a  short  existence  in  a  fused  electrolyte  such  as  he  describes 
where  it  would  be  subject  to  the  action  in  addition  of  nascent  chlorine 
gas.  Numerous  forms  of  sodium  and  potassium  cells  had  their  rise 
and  fall,  the  majority  of  them  being  designed  without  a  suitable 
knowledge  of  the  severe  conditions  and  requirements  for  the  success- 
ful preparation  of  these  metals.  One  of  the  early  workable  designs 
for  a  practical  sodium  cell  was  that  of  Borcher,  which  is  illustrated 
in  Fig.  80.  The  melting-vessel  A  had  an  opening  surrounded  by  the 
socket  tube  B,  and  two  other  openings  with  tubular  necks  C.  The 
double  socket,  which  consists  of  a  porcelain  tube  £,  fits  into  the  socket 
as  shown,  and  this  receives  and  supports  the  upper  chamber  with  its 
electrode  and  side  tube.  This  electrode  is  an  iron  rod,  which  is  made 
the  cathode  of  the  cell,  and  is  immersed  to  a  proper  depth  in  the 
fused  electrolyte.  The  anode  F  is  of  carbon,  and  is  supported  in  a 
porcelain  chamber  provided  with  a  side  tube,  as  shown  at  G.  The 
sodium  separates  upon  the  lower  part  of  the  cathode  and  floats 


THE  ISOLATION  OF  THE  METALS  SODIUM   AND  POTASSIUM.   169 

upward,  where  it  is  allowed  to  overflow  through  the  side  tube  and 
is  collected  in  a  suitable  vessel  containing  a  hydrocarbon.  An 
equivalent  of  chlorine  is  set  free  at  the  anode  and  escapes  by  the  side 
tube  G,  where  it  is  either  allowed  to  escape  into  the  atmosphere  or 
be  utilized  for  the  production  of  a  by-product.  This  particular  piece 
of  apparatus  was  designed  to  take  a  current  varying  between  30  and 
50  amperes,  and  returns  a  yield  of  about  65  per  cent  of  the  weight  of 


FIG.  80. — Borcher's  Design  of  Cell  for  the  Production  of  Sodium  and  Potassium. 


sodium  theoretically  obtainable.  The  principal  objection  to  be 
urged  against  this  apparatus  of  Borcher  is  its  lack  of  durability  and 
costliness  of  its  parts.  It  is  well  known  that  cast  iron  has  but  a 
limited  existence  when  subjected  to  the  action  of  alkaline  chlorides  at 
a  red  heat.  The  porcelain  tube  B,  which  insulates  the  cathode  com- 
partment from  the  electrolytic  cell  is  rather  intricate  in  its  design. 
Although  it  would  be  out  of  place  here  to  give  such  a  minute  and 
detailed  account  of  the  evolution  of  the  sodium  cell  as  will  be  found 
in  special  works  treating  the  subject  of  electrometallurgy  from  the 
commercial  point  of  view,  a  brief  rev  ew  of  the  governing  requirements 
will  be  given.  In  many  of  these  pieces  of  apparatus,  metallic  sodium 


1 70  EXPERIMENTAL  ELECTROCHEMISTRY. 

at  high  temperature  and  porcelain  are  brought  into  direct  contact, 
and  there  must  necessarily  be  a  loss  of  sodium  resulting  from  the 
action  of  the  hot  metal  upon  the  aluminum  silicates  of  the  porcelain. 
According  to  Borcher,  the  following  conditions  must  be  observed  in  the 
successful  design  of  the  electrolytic  cells  for  sodium: 

1.  "A  refractory  metal  only  may  be  used  as  a  material  for  a 
cathode,  preferably  the  better  sorts  of  iron. 

2.  "The   alkaline   metal   must   be   collected   in,    and   conveyed 
from,  the  cathode  cell  without  coming  into  contact  with  any  reducible 
substance. 

3.  "The  walls  of  the  cathode  chamber  may  be  made  to  serve  also 
as  cathodes,  but  in  that  case  they  must  not  be  in  contact  with  the 
electrolyte  on  the  outer  surfaces. 

4.  "The  anode  must  be  made  of  carbon. 

5.  "The  anode  compartment  must  allow  of  an  easy  escape  for 
the  halogen,  and  its  walls  must  be  made  of  some  material  that  will 
withstand  the  action  of  the  halogens  and  haloid  salts. 

6.  "The  walls  of  the  anode  compartment  must  not  be  in  contact 
with  the  separated  metal. 

7.  "No  metallic  object  must  be  immersed  in  the  electrolyte  in 
any  position  between  the  poles  or  in  the  path  of  the  current. 

8.  "The  whole  apparatus  must  be  of  a  fire-resisting  material." 
Without  dwelling  upon  the  very  numerous  forms  and  patterns  of 

sodium  and  potassium  cells,  which  have  met  with  more  or  less  success, 
we  will  describe  the  sodium  cell  as  designed  and  operated  by  Castner, 
which  fulfills  the  conditions  as  tabulated  above  and  has  proved 
itself  to  be  commercially  successful.  Let  us  look  into  the  design  of 
a  workable  Castner  cell  on  a  small  scale,  and  describe  its  mode  of 
operation. 

By  referring  to  Fig.  81,  the  student  may  become  familiar  with  the 
design  of  this  cell,  which  is  here  illustrated  in  elevation  and  section. 
This  particular  experimental  cell  consists  of  a  large  inverted  iron 
bottle  with  a  rather  large  elongated  neck.  An  insulating  stopper 
carrying  an  iron  cathode  is  passed  up  through  the  neck  of  the  bottle, 
which  rests  upon  a  suitable  support  in  order  that  the  bottle  portion 
may  be  heated  by  a  ring-burner.  A  metal  water-jacket  is  slipped 
over  the  lower  part  of  this  neck  in  order  that  the  insulating  stopper 
and  lower  portion  of  the  neck  may  be  kept  cold.  Caustic  soda  or 


THE  ISOLATION   OF  THE  METALS   SODIUM   AND   POTASSIUM.    171 

potash,  as  the  requirements  may  dictate,  is  put  into  the  iron  bottle 
in  a  molten  condition.  That  portion  of  the  fluid  electrolyte  which 
runs  down  into  the  lower  extremity  of  the  neck,  kept  cold  by  the 
water-jacket,  solidifies  and  forms  a  seal  for  the  fluid  portion  of  the 
electrolyte  which  is  kept  at  the  necessary  high  temperature  by  the 


FIG.  81. — Elevation  and  Section  Through  Castner's  Cell.     Experimental  Design. 


ring-burner.  The  anodes  which,  with  the  present  electrolyte,  may 
also  be  of  iron,  are  suspended  from  the  cover,  or  they  may  be  cast  in 
one  piece  of  hollow  cylindrical  form  as  illustrated  in  the  engraving. 
Immediately  over  the  end  of  the  cathode  is  suspended  a  little  cylin- 
drical chamber  or  receiver  for  the  isolated  sodium  or  potassium. 
At  the  lower  extremity  of  this  chamber  we  have  a  cylindrical  wire- 
gauze  guard  which,  because  of  the  high  surface  tension  of  melted 
sodium,  prevents  this  metal  from  flowing  through,  and  thereby  wander- 
ing away  from  the  mouth  of  the  inverted  receiver. 

For  the  removal  of  the  fluid  metallic  sodium,  Castner  uses  a  per- 
forated ladle,  which  retains  the  metal  because  of  its  high  solution 


172 


EXPERIMENTAL  ELECTROCHEMISTRY. 


tension,  while  the  caustic  soda  drains  away  through  the  perforations. 
The  various  parts  of  the  apparatus  are  insulated  by  asbestos.  With 
this  apparatus  hydrogen  gas  is  evolved  at  the  cathode  with  the  sodium, 
accompanied  by  the  expenditure  of  a  certain  amount  of  electrical 
energy.  We  have  escaping  oxygen  gas  from  the  anode  compartment. 
Very  large  quantities  of  metallic  sodium  are  produced  upon  this 
principle.  Fig.  82  shows  the  various  parts  of  such  a  Castner  cell  in 


FIG.  82. — Essential  Parts  of  an  Experimental  Cell  of  Castner's  Type. 


detail,  and  it  will  be  seen  that  they  may  be  easily  made  and  put 
together  by  the  student  in  the  laboratory.  As  will  be  seen  there  are 
only  about  six  or  seven  important  pieces  which  enter  into  the  con- 
struction of  this  laboratory  or  experimental  cell. 

In  order  to  operate  this  furnace  we  should  have,  at  least,  50 
amperes  available  and  a  pressure  of  about  6  volts.  As  will  be  seen 
from  the  following  simple  calculation,  an  electromotive  force  of  4.4 
volts  is  just  sufficient  to  drive  a  current  through  a  fused  sodium- 
hydroxide  electrolyte.  The  heat  of  combination  of  NaOH  is  102 
Calories.  The  minimum  pressure  necessary  therefor  is  obtained  by 
dividing  the  number. of  Joules  represented  by  102  Calories,  by  the  con- 
stant 96,540.  We  will  remember  that  the  Joule  is  equivalent  to 
0.00024  Calorie.  102  divided  by  .00024  gives  us  the  figure  425,000, 

from  which  we  obtain  the  following:  —^ =4-4  volts. 


HE  ISOLATION    OF  THE  METALS   SODIUM   AND   POTASSIUM.  173 

It  is  a  matter  of  interest  to  note  that  hundreds  of  horse-powers 
are  regularly  expended  in  such  sodium  cells  for  the  supply  of  the 
market  of  the  world.  In  our  next  chapter  another  process,  using  a 
fused  electrolyte  and  of  still  greater  commercial  importance,  will  be 
taken  up.  This  will  pertain  to  the  electrolytic  manufacture  of 
aluminum. 


CHAPTER  XII. 
THE  ISOLATION  OF  THE  METAL  ALUMINUM. 

ALUMINUM  is  distinguished  among  metals  as  silicon  is  among 
non-metals  for  its  immense  abundance  in  the  solid  mineral  portions 
of  the  earth,  to  which  indeed  it  is  almost  entirely  confined,  for  it  is 
present  in  vegetables  and  animals  in  so  small  a  quantity  that  it 
can  be  scarcely  regarded  as  forming  one  of  their  necessary  compo- 
nents. Aluminum,  as  we  know,  is  an  extremely  important  element, 
both  in  nature  and  in  the  arts.  It  occurs  very  widely  distributed 
and  very  abundantly  in  many  different  forms  of  combination ;  among 
them  are  feldspar,  mica,  cryolite,  and  bauxite. 

Feldspar  is  a  silicate  of  aluminum  and  potassium,  of  the  formula 
AlKSIsOg.  Mica  is  a  general  name  applied  to  a  large  number  of 
minerals  which  are  silicates  of  aluminum  and  some  other  metal,  as 
potassium,  lithium,  magnesium,  etc.  The  simplest  form  of  mica  is 
that  represented  by  the  general  formula  KAlSiO4,  according  to 
which  the  mineral  is  a  salt  of  orthosilicic  acid,  Si(OH)4.  Cryolite 
is  a  double  fluoride  of  aluminum  and  sodium,  or  the  sodium  salt 
of  fluoaluminic  acid,  NasAIFe.  Bauxite  is  a  hydroxide  of  aluminum 
in  combination  with  a  hydroxide  of  iron.  Besides,  in  the  above 
forms,  aluminum  occurs  in  the  products  of  decomposition  of  minerals. 
One  of  the  most  important  of  these  is  clay,  which  is  found  in  all 
conditions  of  purity  from  the  white  kaolin  to  ordinary  dark-colored 
clay.  Kaolin  is  the  aluminum  salt  of  orthosilicic  acid  of  the  formula 
Al4(SIO4)3  +  4H2O.  Aluminum  silicate  is  found  in  all  soils,  but  is 
not  taken  up  by  plants,  and  does  not  find  entrance  into  the  animal 
body.  The  name  aluminum  has  its  origin  in  the  fact  that  the  salt 
alum  was  known  at  an  early  date,  and  the  metal  was  afterwards 
ioslated  from  it. 

All  the  compounds  of  aluminum  may  be  derived  from  the  oxide 

174 


THE   ISOLATION  OF  THE   METAL   ALUMINUM. 


175 


A12O3  and  the  hydroxide  A12(OH)6.  From  the  oxide  the  sulphide 
Al2Ss  and  the  salts  which  contain  alumina  as  the  base  are  derived, 
and  from  the  hydroxide  the  aluminates  which  are  salts  containing  the 
aluminum  in  the  acid  radical.  The  preparation  of  aluminum  on 
a  large  scale  has  involved  a  problem  of  the  highest  importance  to 
modern  technology.  A  rough  outline  of  the  chemical  means  for 
isolating  this  important  metal  may  not  be  out  of  place.  As  early 
as  1842  Oersted  attempted  the  decomposition  of  aluminum  chloride 
through  the  agency  of  a  potassium  amalgam,  but  the  success  of  his 
work  is  open  to  considerable  doubt,  for  subsequent  workers  endeav- 
oring to  follow  his  directions  were  unsuccessful  in  obtaining  any 
metallic  aluminum.  Three  years  later,  however,  Wohler  successfully 
reduced  the  chloride  by  using  potassium.  Deville  working  at  a  later 
date  produced  this  important  metal  through  aluminum  chloride, 
by  resorting  to  the  use  of  the  double  chloride  of  aluminum  and 
sodium.  Instead  of  the  costly  potassium,  the  far  cheaper  metal, 
sodium,  was  used.  For  twenty-five  or  thirty  years  this  process  was 
carried  on  in  France,  and  for  a  time  it  was  also  used  in  England. 
Rose  in  1853  proposed  the  substitution  of  cryolite  for  the  chloride 
and  used  magnesium  in  the  place  of  sodium.  Grabau's  process,  which 
is  of  much  later  date,  is  of  special  interest,  for  it  is  of  unusual  merit, 
as  may  be  seen  from  the  following  equation,  where  solutions  of  sul- 
phate of  alumina  are  first  treated  with  cryolite  to  obtain  aluminum 
entirely  as  fluoride  A12(SO4)  +Al2F6  =  2Al2F6  +  3Na2SO4.  The  alu- 
minum fluoride  being  insoluble  in.  water,  is  filtered  off,  washed  and 
dried,  and  heated  to  a  low  red  heat,  when  it  is  at  once  charged  into  a 
cold  vessel  lined  with  pure  cryolite.  The  required  quantity  of  metallic 
sodium  is  now  placed  in  upon  the  hot  material  and  the  vessel  covered. 
Accompanied  by  a  great  liberation  of  heat  energy  the  reaction 
takes  place,  which  may  be  represented  by  the  following  equation: 
2Al2F6  +  3Na2=Al2+Al2F6.6NaF.  The  aluminum,  after  the  reac- 
tion has  taken  place,  is  recovered  melted  into  a  metallic  mass  at 
the  bottom  of  the  chamber,  but  covered  over  with  a  slag  of  cryolite, 
which  itself  has  been  completely  fused  through  the  high  temperature 
of  the  reaction.  This  is  a  workable  scheme  for  the  production  of 
aluminum,  but  it  is  evident  at  once  that  the  economy  of  such  a  process 
depends  upon  the  cost  of  sodium. 

The  electrical  production  of  metallic  aluminum  may  be  divided 


i76 


EXPERIMENTAL   ELECTROCHEMISTRY. 


into  two  different  schemes,  one  where  the  metal  is  obtained  by  the 
reduction  of  its  oxide  and  the  other  by  a  typical  case  of  electrolysis. 
Let  us  first  look  into  the  processes  of  reduction.  For  a  long  time 
alumina,  which  is  the  oxide  of  aluminum,  was  held  to  be  unreducible. 
In  the  electric  furnace,  however,  with  sufficient  current  density,  the 
oxide  may  be  reduced  in  the  presence  of  carbon.  This  electro- 
reduction  is  non-electrolytic,  being  simply  brought  about  by  the 


FIG.  83. — Laboratory  Furnace  for  the  Reduction  of  Alumina.      Experimental  Design. 

intense  heat  of  the  electric  furnace.  With  a  sufficient  current  den- 
sity, it  appears  to-day  that  no  oxide  can  withstand  the  high  tempera- 
ture of  the  electric  furnace.  Let  us  impress  upon  a  small  quantity 
of  alumina  this  powerful  reducing  action  of  carbon  at  the  tempera- 
tures accompanying  a  high  current  density  electric  arc.  Fig.  83 
shows  a  handy  laboratory  furnace  for  accomplishing  this.  We  have 
firmly  clamped  in  an  iron  ring  a  graphite  crucible  which  also  rests 
upon  the  iron  base  of  the  ring-stand.  A  large  carbon  rod  fed  through 
an  opening  in  a  fire-clay  cover  serves  as  the  other  electrode.  The 
charge  of  alumina  and  pulverized  carbon  is  placed  in  the  crucible 


THE  ISOLATION   OF  THE  METAL  ALUMINUM. 


177 


around  a  slender  conducting  pencil  of  carbon  to  start  the  electric 
current.  A  very  heavy  current  is  essential  to  bring  about  the  reduc- 
tion. According  to  Borcher,  a  current  density  of  about  3500  amperes 
per  square  inch  will  bring  about  this  reduction.  A  current  of  6500 
amperes  per  square  inch  is  sufficient  to  reduce  any  metallic  oxide 
known.  The  electromotive  force  need  not  be  high,  15  volts  being 
ample  for  a  small  furnace.  About  53  electrical  horse-power  are 
therefore  necessary.  Fig.  84  shows  a  horizontal  furnace  for  the 


FIG.  84. — Furnace  for  the  Reduction  of  Alumina.     Practical  Design. 


reduction  of  alumina  on  a  somewhat  larger  scale.  In  our  small 
crucible  furnace,  the  carbon  pencil  can  be,  of  course,  less  than  an 
inch  in  sectional  area,  permitting  the  use  of  a  smaller  amount  of 
current.  With  one-tenth  of  an  inch  in  sectional  area  for  our  carbon 
pencil,  we  can  reduce  a  small  quantity  of  alumina  with  one-tenth  the 
current  strength.  These  furnaces  are  known  as  resistor  furnaces 
and  are  easily  constructed  and  operated.  Carbon  pencils  of  J 
inch  sectional  area  effect  a  very  complete  reduction  with  a  current 
of  40  amperes.  Let  us  look  into  the  electrolytic  methods  of  isolating 
aluminum,  and  to  this  end  we  will  first  refer  to  Deville's  apparatus. 
The  following  is  a  translation  from  Deville's  original  paper:  "Up 
to  the  present  time  it  has  appeared  to  me  impossible  to  obtain  alu- 
minum from  aqueous  solution  by  means  of  a  galvanic  battery;  and 
I  should  even  now  believe  in  the  absolute  impossibility  of  doing  so 
if  the  brilliant  experiments  of  Bunsen  in  the  production  of  barium, 
chromium,  and  manganese  had  not  shaken  my  convictions.  How- 
ever, I  am  compelled  to  say  that  all  the  processes  of  this  kind  which 
have  been  published  recently  in  reference  to  the  preparation  of 


178  EXPERIMENTAL  ELECTROCHEMISTRY. 

aluminum  have  given  me  only  negative  results.  Every  one  knows 
the  beautiful  process  by  means  of  which  Bunsen  has  produced 
magnesium  by  decomposing  magnesium  chloride  with  the  aid  of  a 
galvanic  battery.  The  illustrious  Professor  at  Heidelberg  has 
opened  a  way  which  may  lead  to  results  that  will  be  interesting  from 
many  points  of  view.  However,  there  can  be  no  hope  of  applying 
the  battery  to  the  direct  decomposition  of  aluminum  chloride, 
which  is  a  substance  which  does  not  fuse,  but  that  volatilizes  at  a 
low  temperature;  it  is  nececsary,  therefore,  to  find  a  composition 
for  the  metallic  bath  that  shall  involve  the  use  of  a  fusible  material, 
from  which  aluminum  alone  can  be  deposited  by  the  electric  current. 
I  have  found  such  a  substance  in  the  double  chloride  of  aluminum 
and  sodium,  the  production  of  which  is  a  necessary  feature  of  the 
extraction  of  aluminum  by  sodium.  This  chloride,  which  is  fusible 
at  about  185°  C.,  and  remains  fixed  at  a  sufficiently  high  tempera- 
ture, although  it  is  volatile  at  a  temperature  above  the  fusing  point 
of  aluminum,  fulfills  all  the  required  conditions.  I  introduced  this 
substance  into  a  porcelain  crucible,  which  was  imperfectly  separated 
into  two  compartments  by  a  plate  of  biscuit  porcelain,  decomposed 
it  by  means  of  a  battery  of  five  elements,  using  carbon  electrodes, 
the  crucible  being  heated  and  the  temperature  being  increased  con- 
tinually in  order  that  the  charge  might  be  maintained  in  a  fluid  con- 
dition as  it  became  gradually  less  and  less  fusible;  but  the  fusing 
temperature  of  aluminum  was  not  exceeded.  Arrived  at  this  point, 
I  stopped  the  experiment,  and,  after  lifting  out  the  diaphragm  and 
the  electrodes,  I  heated  the  apparatus  to  a  bright  red  heat,  and  found 
at  the  bottom  of  the  crucible  a  regulus  of  aluminum,  which  was 
rolled  and  was  exhibited  to  the  Academy  at  its  meeting  on  March 
20th,  1854.  It  was  accompanied  by  a  considerable  quantity  of 
carbon,  which  had  prevented  a  notable  portion  of  the  metal  from 
uniting  into  a  single  mass.  This  carbon  resulted  from  the  disinte- 
gration of  the  very  dense  sample  of  retort  carbon  that  served  as 
electrode;  and  as  a  result  of  this  action  the  positive  electrode  was 
entirely  eaten  away  in  spite  of  its  thickness,  which  was  very  con- 
siderable. This  disposition  of  apparatus  (as  used  by  Bunsen  for 
magnesium)  was  not  convenient  in  the  case  of  aluminum;  and  the 
process  to  which  I  have  been  led,  after  many  experiments,  is  as 
follows:  The  aluminum  bath  is  prepared  by  weighing  2  parts  of 


THE   ISOLATION   OF  THE  METAL  ALUMINUM. 

aluminum  chloride  and  adding  to  it  i  part  of  marine  salt  in  the 
state  of  dry  powder.  The  whole  is  mixed  in  a  porcelain  crucible 
heated  to  about  200°  C.  Combination  shortly  sets  in  with  evolution 
of  heat,  and  there  results  a  very  fluid  mixture,  which  is  a  bath  used 
for  the  decomposition. 

"The  apparatus  [as  shown  in  Fig.  85]  consists  of  a  glazed  porcelain 
crucible  A,  which,  as  a  measure  of  precaution,  is  placed  within  the 
somewhat  larger  fire-clay  crucible  B\  the  whole  is  surmounted  by  a 


FlG.  85.— Deville's  Cell  for  Experimental  Work. 

crucible  cover  C  pierced  with  a  slot  D,  through  which  is  placed  a 
wide  and  stout  sheet  of  platinum  E  to  serve  as  negative  electrode, 
and  with  an  aperture  in  which  is  tightly  fixed  a  well-dried  porous 
cell  F.  Within  the  latter  is  placed  a  rod  of  retort  carbon  G  as  positive 
electrode.  The  bottom  of  the  porous  cell  should  be  kept  at  the 
distance  of  some  centimeters  from  that  of  the  porcelain  crucible. 
The  porcelain  crucible  and  the  porous  cell  are  filled  to  the  same 
level  with  the  fused  aluminum-sodium  chloride,  and  the  apparatus 
is  heated  after  the  manner  described.  The  electrodes  are  then 
introduced  and  the  current  is  passed  through  the  apparatus.  Alumi- 
num is  deposited  with  some  sodium  chloride  upon  the  platinum  plate, 
and  chlorine  together  with  some  aluminum  chloride  is  disengaged 


l8o  EXPERIMENTAL  ELECTROCHEMISTRY. 

in  the  porous  cell;  fumes  are  thus  produced  which  are  destroyed  by 
introducing  dry  and  powdered  marine  salt  at  intervals  into  the 
porous  cell.  This  salt  is  transported  to  the  negative  pole  during  the 
operation  along  with  the  aluminum.  A  small  number  of  elements 
(two  are  actually  sufficient)  are  required  to  decompose  the  chloride, 
which  presents  only  a  feeble  resistance  to  the  electric  current. 

"The  platinum  plate  is  raised  from  time  to  time  as  it  becomes 
sufficiently  charged  with  metallic  and  saline  deposit.  It  is  allowed 
to  cool,  the  mass  of  salt  is  rapidly  broken,  and  the  plate  is  replaced  in 
the  circuit.  The  crude  material  detached  from  the  electrode  is  fused 
in  a  porcelain  crucible  enclosed  within  a  fire-clay  crucible.  After 
cooling,  the  mass  is  treated  with  water,  which  dissolves  a  large  quantity 
of  sodium  chloride;  and  a  gray  metallic  powder  is  left,  which  is 
reunited  into  a  regulus  by  several  successive  fusions.  Addition  of 
<iouble  chloride  of  aluminum  and  sodium  is  necessary  during  each 
fusion." 

This  process  of  Deville  may  be  said  to  have 'marked  the  dawn 
of  the  successful  processes  dependent  upon  the  electrolysis  of  fused 
aluminum  compounds.  As  it  would  require  a  great  deal  more 
space  than  we  are  able  to  give  to  the  subject  in  a  general  work,  to 
enumerate  and  describe  the  various  steps  in  the  evolution  of  alumi- 
num reduction  cells,  we  must  content  ourselves  with  an  outline  of  the 
more  important  processes.  Let  us  look  into  the  method  of  Hall, 
and  for  this  purpose  we  may  best  turn  to  the  specifications  and  draw- 
ings of  one  of  his  patents.  The  following  is  from  the  patent  of  Hall 
of  1886,  and  reads  as  follows:  "The  invention  described  herein 
relates  to  the  reduction  of  aluminum  from  its  oxide  by  dissolving 
such  oxide  in  a  bath  containing  a  fused  fluoride  salt  of  aluminum, 
and  then  reducing  the  aluminum  by  passing  an  electric  current 
through  the  bath,  substantially  as  hereinafter  more  fully  described 
and  claimed.  In  the  accompanying  drawings,  [Fig.  86]  represents  a 
sectional  elevation  of  a  form  of  apparatus  applicable  in  the  practice 
of  my  invention,  and  [Fig.  87]  is  a  view  partly  in  elevation  and  partly 
in  section  of  a  modified  form  of  apparatus. 

"  In  the  practice  of  my  invention  I  prepare  a  bath  for  the  solution 
of  the  aluminum  by  fusing  together  in  a  suitable  crucible,  A,  the 
fluoride  of  aluminum  and  the  fluoride  of  a  metal  more  electro- 
positive than  aluminum,  as,  for  example,  the  fluoride  of  sodium, 


THE   ISOLATION   OF   THE   METAL   ALUMINUM. 


181 


potassium,  etc.,  these  salts  being  preferably  mingled  together  in 
the  proportions  of  84  parts  of  sodium  fluoride  and  169  parts 
fluoride,  represented  by  the  formula  Na2F8.  A  convenient  method 

of  forming  the  bath  consists  in  adding  to  the  mineral  cryolite  —  of 
its  weight  of  aluminum  fluoride.  The  object  of  thus  adding  alu- 


FIG.  86. — Hall's  Electrolytic  Cell  and  Furnace  for  the  Production  of  Aluminum. 


minum  fluoride  is  to  secure  in  the  bath  the  proper  relative  propor- 
tions of  the  fluorides  of  aluminum  and  sodium.  To  the  fused  bath 
is  added  alumina,  or  the  oxide  of  aluminum,  in  sufficient  quantities, 
and  the  alumina  being  dissolved  by  the  fused  bath  an  electric  current 
is  passed  through  the  solution  by  means  of  suitable  electrodes,  C  and 
Z>,  connected  with  a  dynamo-electric  machine  or  other  suitable 
source  of  electricity,  and  immersed  in  the  solution.  By  the  action 
of  the  electric  current,  which  preferably  has  an  electromotive  force 
of  about  4  to  6  volts,  oxygen  is  released  at  the  positive  electrode,  C, 
and  aluminum  is  released  at  the  negative  electrode,  D,  which,  on 
account  of  the  affinity  of  aluminum  for  other  metals,  is  formed  of 


182 


EXPERIMENTAL  ELECTROCHEMISTRY. 


carbon  when  it  is  desired  to  produce  pure  aluminum.  The  positive 
electrode  may  be  formed  of  carbon,  copper,  platinum,  or  other 
suitable  material.  When  formed  of  carbon  the  electrode,  C,  is 
gradually  consumed,  and  must  therefore  be  renewed  from  time  to 
time;  but  when  formed  of  copper  an  oxide  coating  is  formed  over 


N 


FIG.  87. — Experimental  Cell  of  Hall. 

the  surface  of  the  electrode.  This  coating  serves  to  protect  the 
electrode  from  further  destruction  by  the  action  of  the  oxygen,  but 
does  not  interfere  materially  with  the  conducting  qualities  of  the 
electrode. 

"On  account  of  the  affinity  of  the  aluminum  for  other  metals, 
and  also  the  corrosive  action  of  the  materials,  I  prefer  to  form  the 
crucible,  or  melting-pot  A,  of  metal — as  iron  or  steel — and  protect 
the  same  from  the  action  of  the  aluminum  by  a  carbon  lining,  A. 
This  crucible  is  placed  in  a  suitable  furnace,  B,  and  subjected  to  a 
sufficient  heat  to  fuse  the  materials  placed  therein,  such  materials 
fusing  at  approximately  the  same  temperature  as  common  salt. 


THE  ISOLATION  OF  THE  METAL  ALUMINUM.  183 

"  In  lieu  of  the  electrode  D  [Fig.  86],  the  carbon  lining,  A,  may  be 
employed  as  the  negative  electrode,  as  shown  in  [Fig.  87],  the  con- 
ductor from  the  negative  pole  of  the  electric  generator  being  suitably 
connected,  as  shown  at  N,  to  such  lining. 

"In  order  to  render  the  bath  or  solvent  more  fusible,  fluoride 
of  lithium  may  be  substituted  for  a  portion  of  the  fluoride  of  sodium ; 
as,  for  example,  for  one-fourth  the  fluoride  of  sodium  an  equivalent 
amount  of  lithium  fluoride  by  molecular  weights  may  be  substituted. 
Thus  26  parts  of  lithium  fluoride  displacing  42  parts  of  sodium 
fluoride,  the  resulting  combination  contains  26  parts  of  lithium 
fluoride  for  every  126  parts  of  sodium  fluoride,  and  338  parts  of 
aluminum  fluoride. 

"While  I  consider  the  proportions  of  fluorides  of  sodium  and 
aluminum,  and  of  the  fluorides  of  sodium,  lithium,  and  aluminum 
hereinbefore  stated,  are  best  adapted  for  the  purpose,  such  propor- 
tions may  be  varied  within  certain  limits  without  materially  affecting 
the  operation  or  function  of  the  bath,  as  in  fact,  any  proportions 
which  may  be  found  suitable  may  be  employed.  The  aluminum, 
as  it  is  reduced  at  the  negative  electrode,  is  melted  and  collects 
thereon  in  globules,  and  then  drops  down  to  the  bottom  of  the  bath, 
which  is  of  lower  specific  gravity  than  the  molten  aluminum,  and 
can  be  removed  by  suitable  means ;  or  the  bath  may  be  poured  out, 
and  after  being  cooled  the  aluminum  can  be  picked  out." 

Fig.  88  shows  the  scheme  finally  adopted  by  Hall  for  the  pro- 
duction of  aluminum  by  the  electrolysis  of  fused  salts.  According 
to  this  later  patent  the  following  bath  is  employed:  "Fluoride  of 
calcium,  234  parts;  cryolite,  the  double  fluoride  (Na6Al2Fi2),  421 
parts;  the  fluoride  of  aluminum,  845  parts,  by  weight,  and  about 
3  to  4  per  cent  of  a  suitable  chloride,  e.g.,  calcium  chloride.  Alumina 
is  then  added  to  this  bath,  preferably  in  sufficient  quantities  to  form 
a  saturated  solution.  Electrodes  are  then  inserted  in  the  bath,  the 
negative  electrode  being  formed  of  carbon  when  pure  aluminum  is 
desired.  The  positive  electrode  may  be  formed  of  carbon  or  other 
suitable  material.  This  piece  of  apparatus,  as  the  drawing  indicates, 
consists  of  an  iron  trough  lined  with  plates  of  carbon.  A  heavy 
copper  connector  is  riveted  to  the  outside  of  this  trough  and  connects 
with  the  negative  lead  of  the  dynamo.  The  iron  trough,  therefore, 
with  its  carbon  lining  serves  as  a  cathode.  The  anodes  consist' 


1 84 


EXPERIMENTAL   ELECTROCHEMISTRY. 


of  carbon  rods  suspended  from  a  heavy  copper  bar  in  such  a  way 
that  they  may  be  lowered  into  the  electrolyte.  As  these  carbons 
are  slowly  consumed  by  the  oxygen  liberated  in  contact  with  them, 
it  is  necessary  to  have  such  an  adjustment  for  feeding  them  into  the 
bath.  It  is  interesting  to  note  that  with  such  a  system  the  weight  of 
carbon  burned  by  the  nascent  oxygen  is  about  equal  to  the  metallic 
aluminum  produced.  The  carbon  lining  is  but  very  slowly  altered 
and  lasts  for  a  long  time.  The  electrolysis  consists  in  the  decom- 
position of  alumina  dissolved  in  the  fused  bath.  Several  such 
troughs  in  practice  are  connected  up  in  series  for  the  commercial 
production  of  this  important  metal.  In  this  plan  of  operation  the 


FIG.  88. — Hall's  Approved  Aluminum  Cell. 

heat  required  to  keep  the  electrolyte  fluid  is  derived  from  the  elec- 
trolyzing  current.  Immense  quantities  of  aluminum  are  produced 
upon  this  general  principle.  The  next  device  which  we  will  consider 
is  that  of  Heroult,  as  depicted  in  Fig.  89.  This  process  may  produce 
either  metallic  aluminum  or  aluminum  bronze,  the  latter  being 
an  alloy  of  aluminum  and  copper.  In  this  piece  of  apparatus  the 
electrolyte  consists  of  alumina  dissolved  in  fused  cryolite,  or  in  an 
artificial  mixture  of  aluminum  fluoride  with  sodium  fluoride.  The 
electrolyte  is  maintained  in  the  molten  state  by  the  heat  generated 
by  the  passage  of  the  electrolyzing  current.  In  the  illustration  we 
have  a  heavy  iron  vessel  lined  with  carbon  plates,  with  tap-hole 
for  allowing  the  molten  alloy  to  be  drawn  off.  A  heavy  carbon  cover 
with  a  suitable  opening  for  the  anodes  is  put  in  place  to  prevent 
undue  loss  of  heat  from  radiation.  The  anodes  are  connected  as 
shown  to  a  common  holder-bar,  and  are  of  carbon  hung  in  such  a 


THE   ISOLATION   OF  THE   METAL  ALUMINUM. 


185 


way  that  they  may  be  lowered  into  the  electrolyte  as  they  are  con- 
sumed. The  operation  of  the  process  is  started  by  placing  some 
pure  copper  in  the  bottom  of  the  furnace  and  lowering  the  anodes 
until  they  come  in  contact  with  the  metal.  The  intense  heat  of  an 
arc  so  established  fuses  the  copper,  when  the  electrolyte  is  added, 
which,  of  course,  rapidly  assumes  a  fluid  state.  Cryolite  is  added 
until  a  sufficient  depth  has  been  attained  and  the  electrolysis  of  the 


FIG.  89. — Heroult's  Aluminum  Cell. 

alumina  which  is  dissolved  therein  takes  place  between  the  molten 
copper  as  cathode  and  the  immersed  carbon  rods  as  anodes.  Alu- 
minum separates  at  the  molten  copper  and  alloys  with  it,  the  product 
being  allowed  to  run  off  at  intervals.  Additional  quantities  of  copper 
and  alumina  are  fed  in  in  the  proper  proportions  from  time  to  time  to 
form  a  suitable  alloy.  It  may  be  seen  that  the  furnace  and  its  opera- 
tion are  equally  well  adapted  for  the  production  of  pure  aluminum, 
if  some  of  this  metal  is  placed  in  the  bottom  of  the  furnace  instead 
of  copper,  when  the  process  is  first  started,  which  then  approaches 
very  closely  the  device  of  Hall. 


CHAPTER   XIII. 
THE  ISOLATION  OF  CALCIUM. 

CALCIUM  is  more  generally  met  with  in  a  state  of  chemical  com- 
bination than  any  other  metal,  for  it  occurs  in  enormous  quantities 
in  limestones  and  chalks,  and  in  the  minerals  gypsum,  fluorspar, 
apatite,  etc.,  etc.  Yet,  notwithstanding  its  great  abundance  in  com- 
bination, because  of  the  great  difficulties  in  isolating  it,  the  metal  is 
exceedingly  scarce  and  seldom  met  with  in  the  laboratory.  Let 
us  look  a  little  into  the  properties  of  this  interesting  metal,  and  the 
chemical  methods  of  preparing  it,  before  undertaking  to  obtain  it 
by  electrolysis,  which  is  by  no  means  an  easy  task.  Calcium  is 
usually  described  in  the  text-books  as  a  brass-yellow  metal  of  lustrous 
appearance,  which  in  moist  air  soon  becomes  covered  with  a  coating 
of  calcium  hydroxide  and  calcium  carbonate.  Calcium  decom- 
poses water  just  as  potassium  and  sodium  do,  but  the  heat  of  the  re- 
action is  not  sufficient  to  set  fire  to  the  hydrogen  which  it  evolves. 
Calcium,  because  of  the  expense  and  difficulty  in  obtaining  it,  has 
never  had  any  useful  application  except  in  the  most  special  cases 
on  very  small  scales  in  some  research  work.  Before  the  electrolytic 
method  of  isolating  calcium,  it  was  obtained  at  a  great  cost  by  purely 
chemical  means.  The  following  method  will  be  of  interest  to  the 
student  in  general  chemistry  and  will  serve  as  an  introduction  to 
the  electrical  means.  For  example,  calcium  may  be  obtained  as 
a  finely  divided  substance  by  heating  powdered  lime  with  powdered 
metallic  magnesium,  as  shown  by  the  following  simple  equation: 

CaO+Mg  =  MgO  +  Ca. 

After  the  reaction  has  taken  place,  the  presence  of  calcium  may  be 
shown  by  adding  a  little  distilled  water  to  the  mass  in  a  tube,  when 
the  free  calcium  reacting  with  the  water  will  set  hydrogen  free,  and 

186 


THE   ISOLATION   OF   CALCIUM.  187 

in  addition,  the  presence  of  lime-water  in  the  tube  may  be  shown. 
Another  chemical  method  consists  in  making  a  zinc  calcium  and 
distilling  off  the  zinc  by  heating  to  a  high  temperature  in  a  gas-retort 
carbon  crucible.  The  zinc  calcium  is  made  by  melting  together 
a  mixture  of  calcium  chloride,  zinc,  and  metallic  sodium.  The 
sodium  decomposes  the  chloride,  and  the  reduced  calcium  dissolves 
in  the  zinc  as  soon  as  it  is  liberated.  Metallic  calcium  when  heated 
to  redness  burns  with  a  very  brilliant  white  light  and  is  converted 
into  its  oxide.  Modern  text-books  on  general  chemistry  state  that 
it  is  obtained  to-day  by  electrolyzing  its  fused  chloride,  but  they 
do  not,  of  course,  undertake  to  dwell  upon  the  details  of  the  opera- 
tion or  to  even  state  the  great  difficulties  involved.  The  electrolytic 
isolation  of  metallic  calcium  is  far  from  easy,  and  its  electrolytic 
preparation  is  introduced  here  to  show  the  student  in  electrochemistry 
that  his  skill  and  resources  will  often  be  taxed,  and  at  times  very 
severely. 

As  intimated,  therefore,  while  theoretically  simple,  the  extraction 
of  calcium  from  its  chloride  by  electrolysis  is  attended  by  extreme 
difficulty  as  compared  with  certain  other  metals.  It  may  be  stated 
in  general  that  the  three  metals  of  the  alkaline  earths  are  exceedingly 
difficult  to  isolate.  Bunsen  and  Matthiessen  were  the  first  to  isolate 
these  metals  from  their  chlorides  in  their  pure  condition.  Failure 
after  failure  attended  their  efforts  to  extract  these  metals  in  Bunsen's 
laboratory  by  electrolyzing  their  chlorides,  using  apparatus  such  as 
we  described  in  a  previous  chapter  for  the  production  of  metallic 
magnesium  from  its  chloride.  In  the  year  of  1854,  however,  Bunsen, 
as  the  result  of  his  carefully  conducted  research,  was  able  to  point 
put  the  reason  for  the  failures.  The  following  interesting  and  note- 
worthy observation  was  made  by  Bunsen,  which  should  be  impressed 
upon  the  students  of  electrochemistry,  as  Bunsen's  discovery  has 
great  bearing  upon  many  cases  in  this  field.  We  will  quote  his 
own  words,  which  are  as  follows:  "The  density  of  the  current  used 
for  electrolysis — that  is,  the  ratio  of  current  volume  to  electrode — 
area  exerts  a  most  important  influence  on  its  chemical  effects.  The 
power  of  the  current  to  overcome  affinities  increases  with  this  density. 
Of  no  less  importance  is  the  relative  mass  of  the  constituents  of  the 
electrolyte  through  which  the  current  passes."  To  put  Bunsen's 
suggestion  into  practical  operation  we  must  have,  therefore,  means 


1 88  EXPERIMENTAL  ELECTROCHEMISTRY. 

for  electrolyzing  calcium  chloride  and  a  suitable  container  for  the 
same  with  adjustment  for  high  current  density.  It  has  been  found 
in  experiment  and  practice,  that  exceedingly  high  current  density 
at  the  cathode  is  absolutely  essential  for  the  isolation  of  calcium. 
In  order  to  secure  conditions  of  exceedingly  high  cathode  cur- 
rent density  special  designs  of  apparatus  are  necessary.  High 
cathode  current  density  involves  small  cathode  area,  and  a  current 
which  gives  rise  to  very  high  temperature,  even  beyond  the  melting- 
point  of  iron  and  steel.  It  is,  therefore,  necessary  to  provide  some 
means  for  keeping  the  cathode  cold,  or  comparatively  cold.  Means 
must  also  be  provided  for  preventing,  as  far  as  possible,  the  recom- 
bination of  the  liberated  chlorine  with  the  freed  calcium.  The 
device  as  illustrated  in  Fig.  90  embodies  these  set  requirements 
upon  an  experimental  scale.  Here  we  have  a  small  calcium  reduc- 
tion-furnace illustrated  in  both  elevation  and  section.  The  chamber, 
for  the  calcium  chloride  to  be  electrolyzed,  consists  of  a  large  graphite 
crucible,  not  less  than  5  or  6  inches  in  diameter,  with  the  bottom 
sawed  off,  giving  us  in  reality  a  large  graphite  collar.  This  graphite 
crucible  has  clamped  to  its  exterior  a  heavy  iron  band  and  serves 
as  an  anode  in  the  operation.  This  bottomless  crucible,  or  collar, 
rests  upon  and  may  be  cemented  to  a  disk  of  mica,  which  in  turn 
rests  upon  a  cylindrical  water-bath,  as  shown.  This  water-bath  has 
a  tube  soldered  within  its  center,  which  receives  with  a  tight  fit 
the  turned  rod  or  bar  of  iron  not  less  than  an  inch  in  diameter. 
This  rod  is  long  enough  to  go  up  through  the  bottom  of  the  bath  and 
attached  mica  covering,  which  forms  the  bottom  of  the  graphite 
crucible,  extending  a  couple  of  inches  below  and  having  a  stout 
clamp  of  iron  connected  with  the  lead  of  the  dynamo.  The  cathode 
proper  consists  of  a  piece  of  steel  wire  about  1/16  of  an  inch  in 
diameter  and  about  3  inches  in  length,  which  is  securely  screwed 
into  the  upper  end  of  the  iron  bar.  When  the  water-bath  is  filled 
with  cold  water  and  means  provided  for  a  continuous  circulation 
through  it  from  a  spigot,  the  cathode  wire  may  give  up  its  heat  by 
conductance  down  into  the  iron  bar,  which  in  turn  gives  up  its 
acquired  heat  to  the  circulating  water.  In  this  way  it  is  prevented 
from  getting  too  hot.  A  cylinder  of  platinum-wire  gauze  about  ij 
inches  in  diameter  goes  over  the  cathode  wire,  as  shown,  to  prevent 
the  liberated  calcium  from  wandering  about  in  the  electrolyte.  To 


UNIVERSITY 

OF 


THE   ISOLATION   OF   CALCIUM. 


put  such  a  furnace  in  operation  it  is  assembled,  with  the  exception 
of  the  platinum-gauze  cylinder  and  cover,  when  the  cathode  bar  is 


put  in  proper  electrical  connection  with  a  suitable  dynamo.    The 
dynamo  should  be  capable  of  giving  at  least  100  amperes  at  a  pres- 


19°  EXPERIMENTAL  ELECTROCHEMISTRY. 

sure  of  about  60  volts.  The  calcium  chloride  in  lumps  is  slowly 
added,  a  small  quantity  at  a  time,  and  by  means  of  an  iron  rod  a 
small  arc  is  established  between  the  cathode  wire  and  the  side  of 
the  crucible  until  a  small  quantity  of  the  calcium  chloride  has  been 
fused  down  to  a  fluid  state,  which  will  then  conduct  the  electric 
current.  More  chloride  is  added  until  the  crucible  is  about  three 
fourths  filled.  If  means  are  at  hand  for  melting  a  sufficient  quantity 
of  calcium  chloride  separately,  and  pouring  into  the  crucible,  the 
process  may  be  more  quickly  put  in  operation.  When  the  crucible 
is  filled  with  fluid  electrolyte,  the  temperature  is  easily  maintained  at 
the  melting-point  of  the  substance  by  the  current,  and  then  the  plat- 
inum-wire cylinder  should  be  put  in  position.  The  calcium  will  sepa- 
rate in  little  globules  from  the  cathode  and  be  retained  within  the  plat- 
inum-gauze cylinder,  while  the  chloride  will  escape  from  walls  of  the 
crucible,  which  act  as  anode,  and  pass  out  through  the  covering. 
The  author  is  describing  a  successful  run  upon  this  design  of  furnace. 
It  is  very  easy  to  have  an  unsuccessful  run,  and  if  the  conditions  are 
not  just  right  the  attempt  will  result  in  failure.  For  instance,  it 
is  not  really  possible,  so  far  as  the  experiments  of  the  present  writer 
go  to  show,  to  isolate  calcium  with  less  than  60  amperes,  with  a 
design  and  dimensions  similar  to  those  given.  If,  on  the  other 
hand,  too  heavy  a  current  is  used,  the  steel- wire  cathode  will,  in  spite  of 
its  connection  with  the  mass  of  iron  in  the  water-bath,  rise  so  rapidly 
in  temperature  that  it  will  melt  off.  On  the  other  hand,  if  the  cur- 
rent is  not  strong  enough  to  keep  the  entire  mass  in  fusion,  a  solid 
crust  of  calcium  chloride  will  form  on  top  of  the  molten  chloride 
and  offer  a  resisting  seal  to  the  chlorine  gas,  which  is  being  given 
off  from  the  lower  portion  of  the  crucible  walls.  Should  such  a 
crust  form  it  should  immediately  be  punctured  to  allow  the  chlorine 
to  escape,  or  it  will  lift  the  crucible  with  almost  explosive  violence 
from  the  mica  disk,  even  if  it  has  been  securely  cemented  down, 
and  a  stream  of  fluid  electrolyte  will  be  forced  out.  With  everything 
working  smoothly,  the  calcium  may  be  ladled  out  from  the  interior 
of  the  platinum-wire  cylinder  by  means  of  a  small  iron  spoon  per- 
forated to  allow  the  fused  electrolyte  to  run  through,  the  calcium 
remaining  within  the  ladle,  because  of  its  high  surface  tension. 
This  calcium  is  liable  to  take  fire  in  the  air  and  burn  with  a  fierce 
white  light,  and  a  suitable  hydrocarbon  in  a  wide-mouth  vessel 


THE   ISOLATION   OF  CALCIUM. 


191 


should  be  ready  in  which  to  immediately  plunge  the  liberated  metal. 
By  referring  to  Fig.  91  the  separate  essential  parts  of  such  a  laboratory 
furnace  may  be  seen,  which  are,  namely :  a  water-bath,  insulating 
mica  disk  with  a  small  hole  through  its  center,  just  the  size  of  the 
cathode  wire,  and  a  platinum-wire-gauze  cylinder  together  with 
a  heavy  iron  bar  with  its  cathode  screwed  in,  and  a  bottomless 
crucible.  As  the  calcium  industry  is  comparatively  unimportant, 


FIG.  91. — Essential  Parts  of  Experimental  Furnace  for  the  Isolation  of  Calcium. 

we  will  content  ourselves  with  only  one  more  design  of  calcium 
furnace,  and  for  this  purpose  we  will  turn  to  Fig.  92.  This  design 
we  owe  to  Borscher,  as  given  here  in  elevation  and  section.  The 
outer  casing  is  in  the  form  of  a  long  thimble  and  may  be  of  almost 
any  convenient  size.  This  thimble  serves  as  anode,  which  may 
be  of  iron,  brass,  or  nickel.  In  the  bottom  of  this  elongated  thimble 
tube  is  placed  a  small  porcelain  crucible  of  such  a  size  that  it  will 
just  slip  within  the  tube.  The  cathode  is  a  piece  of  steel  wire  between 
1/16  and  1/8  of  an  inch  in  diameter  and  about  i  inch  in  length, 
screwed  into  a  concave  end  of  a  similar  tube  which  is  supported 
by  an  insulating  collar  as  shown.  Within  the  center  of  this  tube, 
which  may  be  supported  by  a  middle  collar  brazed  or  soldered 
in  position,  is  the  cooling  water,  which  falls  directly  upon  the  end 


IQ 2  EXPERIMENTAL  ELECTROCHEMISTRY. 

of  the  tube  carrying  the  cathode  wire,  and  discharging  from  the  outlet 
tube  at  the  right,  as  shown.  With  such  a  device  the  inner  tube 
is  kept  cold,  giving  up  the  heat  generated  at  the  cathode  wire 
which  it  supports.  The  insulating  collar  or  support  is  provided 
with  a  small  side  tube  for  the  escape  of  chlorine  gas.  To  put  the 
furnace  in  operation  the  little  porcelain  crucible  is  dropped  within 
the  elongated  thimble,  and  the  whole  tube  is  filled  about  two 


FIG.  92. — Experimental  Calcium  Furnace.     Borscher's  Design. 

thirds  full  of  calcium  chloride  fragments,  which  may  be  melted  down 
by  holding  the  tube  in  the  flame  -of  a  Bunsen  burner.  When  in  the 
fluid  state,  the  electrolyte  receives  the  water-jacket  tube  and  cathode 
wire,  which,  being  at  a  low  temperature,  immediately  chills  the  cal- 
cium chloride  to  the  point  of  solidification.  This  has  been  indicated 
in  the  drawing  by  the  white  mass  surrounding  the  water-chamber. 
The  cell  is  immediately  placed  in  circuit  with  the  electrical  supply, 
when  the  Bunsen  burner  may  be  removed  and  the  temperature  of 
electrolysis  maintained  by  the  passage  of  the  current.  Calcium  iso- 
lates from  the  steel-wire  cathode  in  small  globules,  and  if  it  rises 
it  is  caught  in  the  concave  end  of  the  water-jacket.  The  little 


THE   ISOLATION   OF  CALCIUM.  IQ3 

porcelain  crucible  serves  a  double  purpose,  namely,  in  catching  any 
metallic  calcium  which  may  fall  if  specific  gravity  conditions  of  the 
electrolyte  so  induce,  but  more  especially  to  prevent  any  chlorine 
gas  from  rising  and  reuniting  with  the  isolated  calcium.  It  will 
be  at  once  appreciated  that  no  chlorine  will  be  liberated  from  the 
interior  of  this  porcelain  crucible,  for  being  of  a  non-conductible 
material  it  does  not  act  as  an  anode.  There  is,  in  consequence,  no 
chlorine  given  off  which  may  reach  the  cathode  at  a  point  lower 
than  the  upper  edge  of  this  crucible.  This  device  of  Borscher  is 
one  intended  for  producing  small  quantities  of  calcium  and  must 
be  directly  taken  apart  in  order  to  secure  such  fragments  of  metal 
isolated.  It  is,  nevertheless,  a  furnace  of  neat  design,  and  very 
useful  for  experimental  work  upon  a  small  scale. 


CHAPTER  XIV. 
THE  ELECTRIC  FURNACE  AND  FURNACE  PRODUCTS. 

ELECTRIC  furnaces  may  be  roughly  classified  into  two  general 
kinds,  those  for  the  attainment  of  moderate  temperatures  and  those 
for  the  attainment  of  the  highest  temperatures  within  the  reach 
of  man.  By  moderate  temperature,  we  may  consider  furnaces 
capable  of  running  up  to  about  1500°  or  1600°  C.  It  is  this  first 
type  of  furnace  which  will  now  occupy  our  attention.  Both  general 
types  of  electric  furnaces  are  converters  of  electrical  energy  into  heat 
energy  and  both  types  depend  upon  resistors.  The  resistors  in  the 
type  of  furnace  which  we  will  consider  first  consist  of  platinum 
wire,  and  because  of  the  facility  and  ease  with  which  the  temperature 
may  be  regulated,  find  a  most  useful  place  in  all  chemical  and  elec- 
trochemical laboratories.  Having  had  considerable  success  with 
the  furnace  here  depicted  it  is  deemed  of  value  to  describe  more  or 
less  in  detail  the  method  of  assembling  and  constructing  such  small 
furnaces  of  a  great  range  of  general  utility.  Fig.  93  illustrates  a 
side  view  of  a  small  mufne  furnace  which  may  be  very  easily  put 
in  operation  and  regulated.  It  consists,  as  shown,  of  an  iron  retort 
stand  with  a  clamp  holding  in  a  horizontal  position  a  fire-clay  tube 
which  is  wound  with  platinum  wire,  having  slipped  over  the  platinum 
wire  winding  a  second  somewhat  larger  fire-clay  tube.  The  terminals 
of  the  platinum  wire  are  connected  with  a  lamp-bank,  together 
with  a  no-volt  or  220- volt  electric  lighting  system.  In  order  to 
make  the  construction  of  this  furnace  clear,  we  will  turn  to  Fig.  94. 
where  the  smaller  tube  is  shown  turned  down  and  spirally  threaded 
to  receive  the  platinum-wire  winding.  It  is  over  this  portion  of  the 
fire-clay  tube  that  the  outer  jacket  is  placed.  There  are  numerous 
kinds  of  fire-clay,  which,  before  baking  may  be  turned  on  the  lathe 
with  facility  and  alter  but  little  in  shape  and  dimension  after  the 

194 


THE  ELECTRIC  FURNACE  AND  FURNACE  PRODUCTS. 


firing  process.  In  this  last  figure  referred  to,  an  end  view  of  the 
furnace  is  given,  together  with  a  side  elevation  of  the  muffle  tube. 
A  good  size  for  such  a  furnace  is  to  have  the  inner  tube,  upon  which 
the  platinum  wire  is  wound,  about  5  inches  long  with  an  internal 
diameter  of  about  ij  inches,  and  an  external  diameter  of  about  2 
inches.  Where  the  tube  has  been  turned  down  and  the  spiral  cut 


FIG.  9^. — Elevation  of  Muffle  Furnace  and  Lamp-bank. 

on,  the  thickness  should  not  be  over  3/16  of  an  inch.  Of  course* 
these  dimensions  may  be  varied  to  meet  different  requirements,, 
but  for  studying  the  behavior  of  certain  bodies  at  different  tempera- 
tures only  a  small  quantity  of  these  bodies  is  necessary  for  the 
examination.  At  least  two  meters  of  platinum  wire  should  be 
wound  on  a  single  furnace,  the  wire  to  be  about  number  22  gauge. 
It  will  require  some  preliminary  experiment  with  each  furnace  in 
connection  with  the  lamp-bank  and  suitable  ammeter  in  series  to 


196 


EXPERIMENTAL   ELECTROCHEMISTRY 


ascertain  how  much  current  the  furnace  will  stand  with  the  out 
side  muffle  in  place.     It  is,  of  course,  an  easy  matter  to  burn  out 


the  platinum  wire,  but  such  a  mishap  is  not  usually  very  serious, 
for  the  wire  is  apt  to  fuse  at  a  certain  point,  when  it  may,  of  course, 


THE  ELECTRIC  FURNACE  AND  FURNACE  PRODUCTS.    19  7 


be  quickly  welded  together  again.     After  a  mishap  of  this  kind 
the  experimenter  will  be  in  possession  of  valuable  data  in  connection 


with  his  furnace  if  he  has  slowly  admitted  the  current  to  it  through 
a  suitable  ammeter.     By  referring  to  Fig.  95  a  sectional  view  through. 


398 


EXPERIMENTAL   ELECTROCHEMISTRY. 


u  completely  assembled  furnace  may  be  seen.  The  furnace  is  here 
indicated  with  a  fire-clay  plug  in  one  end  and  a  similar  plug  of 
light  design  at  the  other  end.  The  furnace  may  be  brought  to 
bright  incandescence  within  a  very  few  moments  after  the  current 
is  turned  on,  and  the  temperature  may  be  held  between  that  of  the 
laboratory  and  the  melting-point  of  platinum  with  great  precision. 
The  temperature  within  the  muffle  tube  can  be  ascertained,  of  course, 
by  the  method  depending  upon  the  melting-point  of  pure  metals,  or 
"by  exploring  the  interior  of  the  furnace  with  a  platinum  loop  carry- 
ing an  electrical  current,  in  connection  with  the  proper  electrical 


FIG.  96. — Top  View  of  a  Vertical  Type  of  Wire  Resistor  Furnace. 

instruments.  A  hint  of  practical  value  may  not  be  out  of  place 
at  this  time.  With  certain  kinds  of  fire-clay  material  there  is 
shrinkage  upon  the  first  firing,  and  the  platinum  wire,  because  of 
its  own  expansion  by  heat,  is  apt  to  come  out  of  the  threaded  groove, 
causing  the  separate  convolutions  of  the  adjacent  coils  to  come 
into  contact  and  cause  serious  trouble  >by  short  circuiting.  This 
may  be  avoided  by  rewinding  the  furnace  after  the  shrinkage  has 
taken  place,  winding  on  the  platinum  wire  quite  tight,  when  there 
will  be  no  more  difficulty  from  this  source. 

Another  design  of  furnace  of  the  platinum- wire  resistor  type, 
is  depicted  in  Figs.  96  and  97.  The  former  being  a  top  view  looking 
down  into  the  furnace  which  is  of  a  vertical  type.  Here  we  have 


THE    ELECTRIC   FURNACE   AND   FURNACE   PRODUCTS. 


199 


a  number  of  small  tubes  or  pipe-stems  arranged  around  the  interior 
of  a  thick  outer  casing  of  fire-clay  and  held  in  position  by  a  fire- 
clay plug  fitting  snugly  in  between  them  and  by  the  lacing  back 
and  forth  of  the  platinum-wire  resistor.  The  second  illustration 
here  shows  a  section  through  the  vertical  type  of  furnace.  With  this 


YiG,  97. — Section  Through  a  Vertical  Type  of  Wire  Resistor  Furnace. 

design  the  platinum  wire  may  expand  without  the  slightest  danger 
of  short  circuits  being  formed,  because  it  is  entirely  enveloped  within 
these  small  vertically  and  cylindrically  arranged  pipe-stems  or 
tubes.  In  experimenting  with  the  platinum  wire  winding  of  an 
electric  furnace  to  ascertain  its  maximum  current-carrying  capacity, 


EXPERIMENTAL  ELECTROCHEMISTRY. 

it  must  be  borne  in  mind  that  the  maximum  current-carrying  ca- 
pacity of  a  platinum  wire  is  very  dependent  upon  its  surrounding 
conditions.  If  we  ascertain  the  current-carrying  capacity  of  the 
platinum  winding  without  the  muffle  tube  in  place  and  then'  give  the 
coil  the  same  current  after  covering  with  the  muffle  tube,  we  will, 
without  question,  burn  out  the  furnace,  for  the  reason  that  the  heat 
can  no  longer  dissipate  so  freely.  It  has  been  found  in  practice 
with  a  furnace  of  the  general  character  of  either  of  the  foregoing 
designs  that  a  platinum-wire  coil  will  stand  only  about  one  half  as 
much  current  when  the  muffle  is  in  place  as  it  did  when  freely 
exposed  to  the  air.  One  must  regard  these  resistor  furnaces  purely 
as  converters,  as  stated  at  the  opening  of  the  chapter,  and  we 
must  maintain  our  furnace  in  operation  at  such  a  point,  where 
the  energy  supply  as  electricity  is  carried  off  as  heat  energy,  the 
balance  between  the  supply  on  the  one-  hand  of  electrical  energy  and 
the  liberation  of  heat  energy  on  the  other  hand,  taking  place  within 
the  limit  of  the  melting-point  of  platinum.  Because  of  the  melting- 
point  of  platinum,  this  design  of  furnace  is  limited  for  work  under 
about  1600°  C.  But  this  vertical  type  may  be  so  modified  as  to 
allow  of  the  temperature  being  carried  up  to  the  very  melting-point 
of  the  fire-clay  itself ,  enabling  the  experimentor  to  melt  down  platinum, 
gold,  iron,  and  steel.  For  this  purpose  this  vertical  pipe  system 
of  tubes  must  be  packed  with  finely  granulated  carbon,  and  instead 
of  being  connected  in  series  must  be  joined  in  multiple-arc  by  con- 
necting all  the  lower  ends  together  by  means  of  a  carbon  disk,  as 
well  as  the  upper  ends  by  means  of  a  similar  carbon  disk.  Such  a 
modified  furnace  will,  of  course,  require  a  very  much  heavier  cur- 
rent to  operate  it,  but  the  suggestion  is  made  here  for  the  benefit  of 
those  who  may  wish  to  experiment  with  small  muffle  furnaces  at 
exceedingly  high  temperatures.  For  the  production  of  electrical 
products  requiring  extremely  high  temperatures  a  furnace  of  very 
different  design  must  be  employed.  Although  at  the  opening  of 
this  chapter  the  author  classified  all  electrical  furnaces  on  the  prin- 
cipal of  suitable  resistors,  the  type  of  furnace  we  are  about  to  describe 
is  sometimes  considered  to  be  of  the  arc  type.  Although  we  may 
have  an  arc  it  may  still  be  maintained  that  this  type  of  furnace  is 
on  the  resistor  principle,  for  in  the  present  case  the  resistor  con- 
sists of  a  stream  of  incandescent  gaseous  carbon.  A  very  convenient 


THE   ELECTRIC   FURNACE   AND   FURNACE   PRODUCTS         201 

laboratory  or  lecture-room  furnace  for  the  production  of  such  bodies 
as   calcium  carbide,  is  illustrated  in  elevation  by  the  photograph 


constituting  Fig.  98.    With  this  practical  design  of  furnace,  which 
was  gotten  up  several  years  ago  by  the  author,  calcium  carbide 


2O2 


EXPERIMENTAL   ELECTROCHEMISTRY. 


may  be  produced  on  the  lecture  table  in  a  very  few  minutes  by 
drawing  only  about  20  amperes  from  a  no- volt  lighting  system. 


Fig.  99  represents  a  sectional  view  through  this  furnace,  but 
it  is  only  by  referring  to  Figs.  100  and  101  that  the  peculiar  design 


THE  ELECTRIC  FURNACE  AND  FURNACE  PRODUCTS. 


203 


of  the  furnace  is  understood.  Here  we  have  6  carbon  electrodes 
so  connected  that  we  have  three  electric  arcs  in  series,  allowing  of 
the  use  of  this  furnace  on  incandescent  lighting  systems,  protected 
only  by  a  fuse  of  moderate  capacity.  It  occurred  to  the  writer  a 
number  of  years  ago  in  wiring  a  couple  of  arc  lamps  across  the 
feeders  of  an  incandescent  lighting  system,  that  a  small  experimental 
electric  furnace  could  be  gotten  up  on  this  plan.  Only  four  carbons 


FlG.  101. — Diagram   Showing   Connections   and  Mode  of  Controlling  Series 
Carbon  Furnace. 


were  employed  at  first  on  the  principle  of  the  two  arc  lamps  in 
series,  but  it  was  found  upon  the  addition  of  such  a  charge  of  lime 
and  coke  as  is  utilized  in  the  production  of  calcium  carbide  that 
it  had  a  decided  short  circuiting  effect  and  allowed  too  heavy 
a  current  to  flow  through  the  furnace.  An  additional  pair  of  carbon 
electrodes  were  then  added,  giving  three  arcs  in  series  instead  of  two. 
With  such  a  furnace  a  suitable  charge  for  the  production  of  cal- 
cium carbide  may  be  employed,  but  the  resistance  to  the  passage 
of  electric  current  is  not  that  offered  by  the  three  small  arcs,  but 
considerably  less,  as  will  be  appreciated  by  any  one  familiar  with 
electricity.  The  resistance  is  sufficiently  high,  nevertheless,  to 


204  EXPERIMENTAL   ELECTROCHEMISTRY. 

enable  one  to  produce  calcium  carbide  in  considerable  quantities 
on  20  amperes  of  current. 

Fig.  101  illustrates  the  connections  of  these  series  carbon  furnaces 


FlG.  102. — Vertical  Type  of  Furnace  with  a  single  Arc. 


coupled  with  a  variable  rheostat  for  controlling  the  intake  of  cur- 
rent by  the  furnace.  If,  however,  ample  current  is  at  hand, 
say  50  or  60  amperes,  a  double  crucible  furnace,  like  that  illustrated 
in  Fig.  102,  is  found  very  convenient.  Here  we  simply  have  two  cru- 


THE  ELECTRIC  FURNACE  AND  FURNACE  PRODUCTS.    205 

cibles,  one  within  the  other,  separated  by  some  good  non-com- 
bustible heat  insulating  material.  With  this  equipment,  calcium 
carbide,  carborundum,  etc.,  may  be  prepared  on  a  small  scale. 
For  the  reduction  of  metallic  oxides  in  the  presence  of  carbon  this 
type  of  furnace  is  most  convenient.  For  the  production  of  quanti- 
ties of  calcium  carbide  on  a  small  scale  on  the  lecture  table  the 
following  directions  should  be  carefully  followed:  Good  unslacked 
lime  and  hard  carbon  are  weighed  out  in  the  requisite  combining 
proportions.  The  following  equation  indicates  theoretically  the  pro- 
duction of  calcium  carbide,  and  from  the  same,  the  amounts  to  be 
weighed  out  may  be  learned  • 

CaC2  +  CO. 

By  hard  carbon,  it  is  meant  that  charcoal  be  not  employed,  for  be- 
cause of  its  lightness  it  is  apt  to  burn  away  without  combining 
with  the  calcium  of  the  lime.  A  convenient  and  most  satisfactory 
carbon  is  obtained  by  crushing  up  in  a  large  mortar  fragments  of 
old  electric  light  carbons.  Both  the  carbon  and  the  lime  should 
be  ground  to  a  fine  granulation  and  intimately  mixed  together,  and 
for  this  purpose  the  writer  has  found  an  old  iron  coffee-mill  to  meet  the 
requirements  in  a  most  satisfactory  manner.  After  a  run  of  half  an 
hour  at  a  full  incandescent  temperature,  fragments  of  calcium  car- 
bide will  be  obtained  as  large  as  an  English  walnut,  which  yield  a 
large  supply  of  gas,  and  may  be  burned  in  a  large  jet  if  thrown 
into  a  cylinder  jar  of  water  equipped  with  a  small  glass  outlet  tube 
and  tight  fitting  stopper.  As  we  experiment  with  hydrogen  the 
jet  should  not  be  lighted  until  one  is  sure  that  all  of  the  air  has  been 
driven  from  the  cylinder.  It  must  be  remembered  that  the 
preparation  of  calcium  carbide  requires  extreme  temperature.  The 
furnace  must  be  allowed  to  be  well  under  way  in  temperature  before 
the  timing  of  the  run  is  begun.  An  electric  furnace  of  this  type  is 
nothing  more  or  less  than  a  box  of  poor  heat  conducting  material, 
in  which  electrical  energy  is  poured,  so  to  speak,  until  the  entire 
interior  assumes  a  temperature  of  the  electric  arc.  The  temperature 
of  the  arc  has  been  carefully  computed  by  many  experimenters 
and  is  found  to  be  in  the  neighborhood  of  3500°  C.,  which  is  6332°  F. 
We  will  not  go  into  the  commercial  question  of  electrical  furnaces 


206  EXPERIMENTAL  ELECTROCHEMISTRY. 

here  as  it  would  constitute  a  treatise  in  itself.  We  are,  nevertheless, 
fully  enabled  at  this  time  and  at  this  stage  of  our  work  to  conduct 
an  efficiency  research  upon  electrochemical  processes  of  this  kind, 
if  we  have  profited  by  the  previous  chapters  on  the  theoretical  side 
of  our  subject.  Believing  that  we  have  here  outlined  the  simplest 
types  of -electric  furnace  available  for  experimental  work,  we  will 
take  up  another  subject  in  the  next  chapter. 


CHAPTER  XV. 
PREPARATION  OF  ORGANIC  COMPOUNDS. 

THE  ELECTROLYSIS  OF  SODIUM  ACETATE. 

IN  the  present  chapter  we  will  produce  electrolytically  certain 
organic  chemical  compounds,  and  we  will  start  our  work  by  taking 
a  typical  case  of  organic  electrolysis  and  one  of  peculiar  beauty 
for  demonstration  purposes,  as  a  combustible  gas  is  set  free  at  each 
electrode.  To  accomplish  this  we  will  electrolyze  a  strong  solution 
of  sodium  acetate:  CH3.COONa  in  the  assembled  apparatus,  as 
illustrated  in  Fig.  103.  Here  we  have  at  A  the  electrolytic  cell, 
which  consists  of  a  wide  mouth  glass  cylinder,  carrying  a  large 
rubber  stopper.  Through  the  center  of  this  rubber  stopper  is  a 
glass  tube  of  large  diameter  terminating  in  a  bell  mouth,  as  shown 
at  B.  This  glass  tube,  which  is  somewhat  the  shape  of  a  lamp- 
chimney,  is  provided  with  a  tight  fitting  stopper  at  its  top  through 
which  passes  the  wire  attached  to  the  anode  and  the  glass  tube  C, 
leading  to  the  wash-bottle  F  and  gas-collecting  tube  D  at  the  extreme 
left.  Immediately  under  the  bell-mouth  opening  of  the  tube  B  is 
a  cylindrical  porous  pot  E  containing  the  anode  G,  which  is  of 
platinum.  The  cathode  H  is  a  large  cylinder  of  pure  sheet  copper 
surrounding  the  porous  pot  E  and  leaving  considerable  space  for 
electrolyte  between  it,  the  walls  of  the  outside  containing  vessel 
and  the  porous  pot.  The  tube  /  passes  through  the  stopper  of 
the  outside  container,  the  electrolytic  cell  A  and  runs  to  the  bottom 
of  the  wash-bottle  J,  thence  to  the  vertical  gas  collecter  K.  The 
wash-bottle  /  contains  plain  water,  whereas  wash-bottle  F  contains 
lime-water  for  the  absorption  of  carbon  dioxide.  The  terminals 
of  the  electrolytic  cell  are  connected  to  the  lighting  system  through 
our  lamp-bank  and  two  or  three  i6-c.p.  lamps  will  suffice  for  the 

207 


203 


EXPERIMENTAL   ELECTROCHEMISTRY. 


current.      At   the   cathode   we   will  have   two  atoms   of  hydrogen 
isolated,  as  a  result  of  the  setting  free  of  sodium,  as  shown  by  the 


(    P!i|.!ili!» 


secondary  react.ion  in  the  following  equation : 

2Na  +  2H2O  -  2NaOH  +  2H. 


PREPARATION   OF   ORGANIC   COMPOUNDS.  209 

This  hydrogen  will,  of  course,  be  collected  in  the  tube  K  after  pass- 
ing through  the  wash-bottle  /.  At  the  anode  the  following  processes 
take  place : 

2CH3.COO    +H20  =  2CH3.COOH  +  0, 
2CH3.COOH  +  O      -  C2H6  +  2CO2  +  H2O. 

The  gas  ethane  C2H6,  and  carbon  dioxide  CO2  escape  through 
the  tube  C.  The  carbon  dioxide  is  absorbed  by  the  lime-water 
with  the  formation  of  calcium  carbonate,  whereas  the  ethane  col- 
lects in  the  vertical  tube  D.  It  is  interesting  to  note  that  the  volume 
of  ethane  is  about  the  same  as  the  volume  of  hydrogen  produced. 
According  to  Jahn,  we  would  obtain  more  ethane  if  it  were  not 
for  the  oxidation  of  some  of  the  acetic  acid  at  the  anode  by  the 
oxygen,  as  suggested  by  the  following  equation : 

CH3.COOH  +  4O  =  2CO2  +  2H2O. 

The  hydrogen  and  ethane  produced  may  be  ignited  to  show 
that  both  gases  are  of  a  combustible  nature. 

THE   ELECTROLYTIC    PRODUCTION   OF   IODOFORM. 

For  the  production  of  iodoform  we  will  require  a  beaker  of 
about  500  cubic  centimeters  capacity,  a  cylinder  of  nickel  wire  gauze 
to  serve  as  cathode,  a  porous  pot  and  a  suitable  platinum  anode. 
The  beaker  is  to  be  mounted  upon  a  tripod  in  order  that  the  process 
may  be  conducted  at  an  elevated  temperature.  Free  iodine  when 
allowed  to  react  with  a  heated  aqueous  alkaline  solution  of  ethyl 
alcohol  produces  iodoform,  (CHI3.)  Fig.  104  shows  the  assembled 
apparatus  with  a  thermometer  for  observing  the  temperature  of 
the  reaction.  The  nickel  gauze  cylinder,  porous  pot,  and  anode 
are  also  separately  shown  at  the  right  in  this  illustration.  Without 
taking  into  account  the  intermediate  products  formed,  the  reaction 
may  be  expressed  very  simply  by  the  following  equation: 

CH3CH2OH  + 10!  +  H2O  =  CHI3  +  CO2  +  yHI. 

One  will  observe  that  we  have  hydriodic  acid  formed,  which,  of 
course,  will  combine  with  the  sodium  hydroxide  present  to  produce 
sodium  iodate  and  carbonic  acid.  The  following  directions  for 
the  actual  carrying  out  of  an  experiment  may  be  followed  to  advan- 
tage: The  cathode  of  nickel-wire  gauze  is  placed  in  the  beaker, 


2IO 


EXPERIMENTAL   ELECTROCHEMISTRY. 


together  with  the  cathode  liquid,  which  consists  of  a  strong  solution 
of  sodium  hydroxide.  Within  the  porous  pot,  which  is  next  placed 
in  position  is  a  solution  consisting  of  15  grams  of  sodium  hydroxide, 
10  grams  of  potassium  iodide,  10  cubic  centimeters  of  ethyl  alcohol, 
and  100  cubic  centimeters  of  distilled  water.  The  thermometer  is 


FIG.   104.— Apparatus  for  the  Electrolytic  Production  of  lodoform. 


placed  within  the  porous  pot  and  the  temperature  elevated  to  about 
70°  C.  The  best  working  current  density  at  the  anode  for  this 
preparation  is  about  one  ampere  per  square  decimeter.  It  is  well 
to  allow  the  current  to  run  for  4  hours,  when  the  process  may  be 
interrupted.  The  liquor  from  the  interior  of  the  porous  pot  is 
poured  out  into  an  evaporating  dish,  when  after  standing  for  some 


PREPARATION   OF   ORGANIC   COMPOUNDS.  21 1 

time,  from  i  to  2  hours,  a  beautiful  crystalline  deposit  of  iodoform 
is  filtered  off  and  allowed  to  dry  at  the  temperature  of  the  laboratory. 
There  will  be  formed  as  a  secondary  product  in  the  mother  liquor,, 
sodium  iodate.  The  yield  of  iodoform  is  about  70  per  cent.  This 
is  a  very  satisfactory  organic  preparation,  and  lends  itself  to  some 
interesting  efficiency  determinations  when  conducted  in  connection 
with  suitable  electrical  measuring  instruments. 

THE   ELECTROLYTIC   PRODUCTION   OF   CHLOROFORM. 

Chloroform  may  also  be  prepared  electrolytically.  For  this 
purpose  a  suitable  still,  which  may  be  heated  by  a  steam  jacket 
and  containing  a  set  of  revolving  paddles,  is  employed.  These 
paddles  consist  of  carbon  plates  and  are  made  the  anode  in  the 
electrolytic  process.  The  interior  of  the  still,  which  must  be  of 
lead,  serves  as  cathode.  A  20  per  cent  solution  of  common  salt 
is  placed  in  the  still  to  which  acetone  is  admitted  from  the  bottom, 
as  shown,  by  means  of  the  tube  which  leads  to  the  elevated  reservoir. 
The  acetone  is  converted  into  chloroform  by  the  combined  action 
of  chlorine  and  sodium  hydroxide.  The  reaction  may  be  theoretically 
illustrated  in  two  stages  according  to  the  following  equations: 

(1)  (CH3)2CO+3C12  =  CH3COCCI3  +  3HCI; 

Chloracetone. 

(2)  CH3COCCI3  +  NaOH  =  CH3COONa  4-  CHC13. 

Sodium  Acetate.       Chloroform. 

The  chloroform  produced  distils  off  because  of  the  elevated  tempera- 
ture maintained  by  the  live  steam  and  is  collected  in  a  suitable 
receiver.  It  is  claimed  that  from  100  parts  by  weight  of  acetone 
1 80  parts  by  weight  of  chloroform  are  produced.  The  theoretical 
yield  figures  out  206  parts  by  weight  of  chloroform,  so  it  will  be 
seen  that  the  process  is  quite  economical.  It  is  interesting  to  note 
from  a  study  of  these  equations  that  only  one  of  the  two  available 
methyl  groups  in  the  acetone  is  utilized  for  the  production  of  chloro- 
form. In  the  drawing,  Fig.  105,  it  will  be  observed  that  the  current 
is  sent  into  the  revolving  anodes  by  means  of  a  brush  and  the  com- 
mutator. 

THE   PRODUCTION   OF   ACETYLENE. 

There  is  to-day  a  big  field  for  the  organic  chemist  with  refer- 
ence to  electricity.  Seme  of  the  reactions  brought  about  by  the 


212 


EXPERIMENTAL  ELECTROCHEMISTRY. 


aid  of  electricity  possess  the  greatest  field  for  synthetic  organic 
chemistry.  Berthelot  showed  that  carbon  and  hydrogen  combined 
to  form  acetylene  on  causing  the  electric  arc  to  pass  between  carbon 
electrodes  in  an  atmosphere  of  hydrogen. 


For  this  purpose  a  glass  globe  was  employed  with  two  openings 
opposite  each  other  in  the  form  of  tubulures,  into  which  were  fitted 


FIG.   105. — Apparatus  for  the  Production  of  Chloroform  Electrolytically. 


large  stoppers  carrying  electrodes  and  entrance  and  exist  tubes 
for  the  gas.  The  globe  was  first  carefully  swept  free  of  air  by  a 
current  of  hydrogen  when  an  electric  arc  was  established  through 
the  carbon  pencils  within.  A  good  yield  of  acetylene  results  from 
such  a  combination.  This  is,  of  course,  simply  of  scientific  interest 
and  has  no  practical  application.  The  following  organic  synthesis, 
however,  is  not  only  of  scientific  interest  in  the  experimental  labora- 


PREPARATION   OF   ORGANIC   COMPOUNDS.* 


213 


tory,  but    has    found  a  commercial    application.     It   pertains    to 
the  production  of  carbon  disulphide  in  the  electric  arc. 

THE   PRODUCTION  OF   CARBON  DISULPHIDE. 

If,  instead  of  supplying  hydrogen  to  the  enclosed  electric  arc 
between  carbon  electrodes,  we  supply  sulphur  or  roll  brimstone 
we  get  quite  another  product,  namely:  The  mobile  and  volatile 
liquid,  known  as  carbon -disulphide.  This  interesting  compound 
may  be  prepared  upon  an  experimental  scale  by  assembling  and 
-operating  such  a  piece  of  apparatus  as  illustrated  in  Fig.  106.  Here 


FlG.  106. — Glass  Globe,   Carbon  Electrodes  and  Sulphur  for  the  Experimental 
Production  of  Carbon  Disulphide. 

we  have  a  large  glass  globe  equipped  with  four  tubulures  or  necks 
to  receive  stout  stoppers.  A  metal  rod  with  insulating  handle  passes, 
as  indicated,  through  two  of  these  tubulures  in  a  horizontal  position, 
terminating  in  holders  for  supporting  carbon  pencils.  Before  these 
stoppers  are  put  in  place  a  narrow  strip  of.  thin  asbestos  is  drawn 
through  and  held  in  position  as  a  bridge  by  the  stoppers  which 
carry  the  electrodes.  Upon  this  piece  of  asbestos,  between  the  ends 


214  EXPERIMENTAL   ELECTROCHEMISTRY. 

of  the  carbon  electrodes,  the  roll  brimstone  is  placed.  The  globe 
is  swept  out  by  carbon  dioxide  gas  and  the  arc  is  started  between 
the  carbon  pencils.  Carbon  disulphide  in  the  state  of  a  gas  is 
formed  within  the  arc,  condensing  in  minute  drops  over  the  interior 
surface  of  the  glass  globe.  After  a  suitable  run,  enough  carbon 
disulphide  will  condense  to  run  to  the  bottom  of  the  globe,  where 


FIG.   107.— Experimental  Equipment  Complete  for  the  Preparation  of 
Carbon  Disulphide. 

it  flows  out  through  the  bottom  opening  and  may  be  collected  in  a 
test-tube.  So  much  for  the  experimental  side  of  this  work.  It  will 
be  of  interest  to  know  that  this  process  is  being  carried  on  upon  a 
commercial  scale  in  New  York  State  where  specially  designed 
furnaces  are  in  operation.  These  furnaces,  erected  at  Penn  Yan, 
are  16  feet  in  diameter  and  41  feet  high.  The  process  as  carried 
on  by  Taylor  originally  consisted  in  building  a  furnace  with  an 
experimental  shell  of  iron,  in  which  the  brimstone  is  placed  and 
melted  down  by  the  heat  radiated  from  the  inner  metal  shell  of  the 
furnace  where  the  electric  arc  had  been  maintained.  Brick  walls 
were  subsequently  substituted  for  those  of  metal  and  the  sulphur 
in  the  cold  state  fed  directly  to  the  furnace  surrounds  the  interior 


PREPARATION   OF  ORGANIC   COMPOUNDS.  215 

so  completely  as  to  practically  make  a  blanket,  which,  in  melting, 
carries  back  into  the  furnace  the  heat  absorbed.  This  regeneration 
proved  to  be  efficient  in  the  extensive  production  of  carbon  disul- 
phide.  It  is  said  that  in  a  building  containing  the  furnace  there 
are  no  unpleasant  gases  that  are  in  the  least  in  evidence,  the 
entire  building  being  at  times  as  comfortable  as  any  ordinary; 
manufacturing  plant;  in  fact  other  operations  could  be  conducted 
within  the  same  building  without  inconvenience.  Arrangements 
were  made  in  this  process  to  keep  the  electrodes  constantly  and 
automatically  supplied  with  broken  carbon  which  provides  the 
electrodes,  themselves  of  carbon,  with  large  contact  surface, 
from  which  the  broken  carbon  tapers  off  to  the  interior  of  the  fur- 
nace where  the  current  resistance  converts  the  electrical  energy 
into  heat  just  where  it  is  required  for  effective  work.  The  sulphur 
rises  in  the  bottom  of  the  furnace,  and  its  heat  is  regulated  by  feed- 
ing cold  sulphur  into  the  surrounding  chamber  to  meet  the  require- 
ments. The  sulphur,  being  a  non-conductor  of  electricity,  itself 
plays  an  important  part  in  regulating  the  amount  of  current  which 
flows  through  the  furnace.  The  alternating  current  is  used  in  Mr. 
Taylor's  furnace,  which  has  practically  revolutionized  the  manufac- 
ture of  carbon  disulphide  in  America. 


ELECTROLYTIC  OXIDATION. 
THE   PREPARATION   OF    KANARIN. 

As  we  learned  in  a  previous  chapter,  oxidation  and  reduction  may 
be  effected  by  the  proper  adjustment  of  current  density,  etc.,  and 
we  will  now  apply  this  important  electrolytic  oxidation  method  for 
the  practical  production  of  certain  organic  oxidation  products. 
Organic  electrolysis  may,  in  the  majority  of  cases,  be  divided  into 
two  general  processes  entirely  independent  of  current  density  con- 
ditions. On  the  one  hand  we  will  have  oxidation,  and  on  the  other 
we  will  have  reduction.  Therefore,  most  cases  of  organic  electrolysis 
are  either  oxidation  or  reduction  processes.  The  electrolysis  of 
organic  compounds  is  of  comparatively  recent  development,  and  a 
sound  knowledge  of  organic  chemistry  is  essential  for  work  in  the 
new  field  of  organic  electrochemistry.  It  would  be  impossible  in  a 


216  EXPERIMENTAL   ELECTROCHEMISTRY. 

general  experimental  work  on  this  subject  to  go  deeply  into  the 
chemistry  and  electrochemistry  of  organic  oxidation  or  reduction 
products,  and  we  will  content  ourselves  by  introducing  one  or  two 
experiments  which  illustrate  the  effect  of  the  electric  current  upon 
organic  compounds  when  applied  under  proper  conditions.  Per- 
haps the  production  of  the  organic  yellow  dye,  known  as  kanarin, 
will  serve  best  to  illustrate  a  typical  case  of  organic  oxidation.  For 
carrying  out  an  actual  experiment  we  will  employ  a  Hoffman  appara- 
tus of  a  general  type,  which  is  shown  by  the  photograph  in  Fig.  108. 
For  this  experiment  the  Hoffman  apparatus  is  provided  with  plati- 
num electrodes,  and  the  electrolyte  consists  of  a  solution  of  potassium 
sulphocyanide  in  the  proportion  of  one  part  by  weight  of  the  sul- 
phocyanide,  and  five  parts  by  weight  of  distilled  water.  This  solution 
is  placed  within  the  Hoffman  apparatus,  the  terminals  of  which 
connect  through  two  or  three  i6-c.-p.  lamps  to  the  lamp-bank  and 
loo-volt  lighting  system.  Hydrogen  is  given  off  at  the  cathode 
and  streams  up  through  the  solution  in  the  cathode  tube  of  the 
Hoffman  apparatus,  where  it  collects,  as  in  the  ordinary  case  of 
electrolysis  of  dilute  sulphuric  acid.  The  interesting  optical  feature 
of  this  experiment  is  the  non-appearance  of  the  corresponding 
oxygen  at  the  anode.  Here  we  have,  therefore,  hydrogen  streaming 
off  the  cathode  and  collecting  in  the  cathode  tube,  with  no  gas 
liberated  at  the  anode,  for  the  oxygen  set  free  immediately  oxidizes 
and  combines  with  the  sulphocyanide  acid  to  produce  kanarin, 
which  appears  as  a  yellow  mass  extending  over  the  surface  of  the 
anode.  The  theory  of  this  oxidation  may  be  represented  by  the 
following  equation  : 

6HCNS  + 1  iQ  +H2O  =  C6H4O2N4S5  +  H2SO4  +  2HNO3. 

The  kanarin  which,  after  fifteen  or  twenty  minutes,  will  have 
collected  in  sufficient  quantities  for  an  experiment  in  dyeing,  for 
which  purpose  the  kanarin  is  dissolved  in  a  basic  solution. 

CASES  OF  ELECTROLYTIC   REDUCTION. 

Let  us  now  look  into  a  case  of  reduction,  and  for  this  purpose 
we  will  choose  nitrobenzene.  The  nitrobenzene  is  first  dissolved 
in  strong  sulphuric  acid  and  placed  in  a  porous  pot,  into  which  a 


PREPARATION   OF   ORGANIC   COMPOUNDS. 


217 


platinum  cathode  is  immersed.  The  anode,  of  platinum,  is  placed 
outside  the  porous  pot  in  an  80  per  cent  solution  of  sulphuric 
acid  in  distilled  water.  The  porous  pot  with  its  cathode  and 


FIG.   108. — Hoffman's  Apparatus  which  Deserves  a  Special  Place  of  Honor  in 
Electrochemical  Work. 

the  anode  are  placed  within  a  larger  beaker  glass  and  the  electric 
current  turned  on.  The  product  is  para-amido-phenol  sulphonic 
acid  of  the  following  chemical  composition:  CeH^NH^OH). 
The  reaction  within  the  cell  is  believed  to  take  place  in  two  stages, 


21  8  EXPERIMENTAL  ELECTROCHEMISTRY. 

as  shown  in  the  following  equations  with  the  intermediate  production 
of  phenylhydroxylamine  : 


C6H5(N02)  +2H2  =  C6H5(NH)(OH)H20; 

Phenylhydroxylamine. 

C6H5(NH)  OH       =  C6H4(NH2)  (OH)  . 

Amido-phenol. 

The  ultimate  product,  which  is  para-amido-phenol  sulphuric  acid, 
separates  from  the  electrolyte  in  the  form  of  fine  crystals,  which 
are  filtered  off  through  asbestos.  To  illustrate  the  working  range 
of  organic  electrolytic  reduction  it  may  be  well  to  refer  to  two  other 
preparations  by  the  reduction  of  nitrobenzene.  Nitrobenzene,  when 
in  a  diluted  sulphuric  acid  solution,  yields  under  similar  conditions 
of  electrolysis,  the  aniline  direct  as  shown  by  the  following  equation  : 

C6H5(N02)  =C6H5(HNH2)  +2H20. 

When  nitrobenzene  is  in  an  alkaline  solution  azobenzene  is  produced, 
as  shown  by  the  following  equation  : 

2C6H5(N02)H8  -  C6H5NNC6H54H20. 

Such  reductions  may,  of  course,  be  br6ught  about  by  ordinary 
chemical  means,  but  with  the  electrolytic  process,  there  are  many 
outside  points  in  its  favor,  among  which  may  be  mentioned  an 
ease  of  control  of  the  course  of  the  reaction.  There  are,  however, 
cases  where  electrolytic  reduction  brings  about  results  different 
from  those  obtainable  by  ordinary  chemical  means.  It  will  now 
be  seen  from  the  fundamental  and  typical  cases  given  here,  that 
oxidation  and  reduction  in  cases  of  organic  electrolysis  do  not 
depend  so  much  upon  conditions  of  current  density  at  anode  or 
cathode,  but  more  especially  upon  the  composition  of  the  electrolyte 
itself.  The  cases  that  might  be  here  cited  in  the  field  of  organic 
chemistry  are  almost  without  limit,  and  we  must  content  ourselves 
in  the  present  work  with  the  typical  cases  presented. 


CHAPTER  XVI. 
THE  PRIMARY  CELL. 

IN  the  present  chapter  we  will  deal  with  the  production  of  the 
electric  current  through  chemical  action,  and  this  phenomenon  may 
be  regarded  as  the  converse  of  what  we  have  hitherto  considered. 
We  have,  up  to  the  present  time,  applied  the  electric  current  to  com- 
pounds in  a  state  of  solution,  and  we  will,  in  the  present  chapter,  look 
into  the  production  of  the  electric  current  by  the  chemical  action  of 
substances  in  solution  within  a  suitably  arranged  and  assembled  cell. 
Two  great  problems  in  electrochemistry  presented  themselves  to  the 
early  workers  in  this  field,  the  first  being:  How  does  the  electric 
current  decompose  electrolytes  and  what  is  the  mechanism  of  such 
decomposition,  which  we  term  electrolysis  ? 

The  second  problem  relates  to  the  origin  of  the  electric  current. 
What  produces  it,  and  how  can  we  satisfactorily  explain  the  phenom- 
ena observed  when,  for  example,  dissimilar  metals  are  immersed  in 
an  acid?  We  have  already  considered,  at  considerable  length,  the 
decomposition  side,  or  electrolysis,  when  compounds  are  subjected 
to  the  influence  of  the  electric  current. 

In  our  very  first  chapter  we  touched  upon  the  origin  of  the 
electric  current  in  a  general  way  and  referred  to  the  work  of  Galvani 
with  his  frogs,  and  also  to  Professor  Fabroni,  of  Florence,  as  well 
as  to  Alexander  Volta,  of  Pavia.  For  the  sake  of  historic  interest, 
and  also  to  illustrate  to  the  student  the  hopeless  condition  of 
affairs  pertaining  to  the  origin  of  the  electric  current,  we 
will  turn  for  an  instant  to  the  time  when  Galvani  and  his  famous 
experiments  upon  frogs  attracted  the  attention  of  the  scientific 
world.  It  will  be  remembered  that  in  the  famous  experiment  of 
Galvani,  conducted  in  the  year  1786,  the  dawn  of  dynamic  electricity 
was  marked.  It  is  true  that  six  years  prior  to  this,  Galvani  observed 

219 


220  EXPERIMENTAL   ELECTROCHEMISTRY. 

that  the  limbs  of  dead  frogs  when  hung  upon  a  copper  hook  in  the 
neighborhood  of  a  frictional  electric  machine  contracted  violently 
at  each  spark  or  discharge  of  the  then  known  static  electricity. 
It  is  the  later  experiment,  however,  conducted  in  1786,  which  we 
may  refer  to  as  the  first  to  attract  universal  attention.  It  will  be 
remembered  that  Galvani  obtained  the  twitching  of  the  limbs  of 
dead  frogs  without  the  agency  of  any  electrical  machine  whatever, 
by  bringing  a  copper  wire  joined  to  a  nerve  in  contact  with  a  piece 
of  iron  'wire,  which  was  attached  to  one  of  the  limbs  of  the  frog. 
The  analogy  of  these  results,  although  six  years  apart,  nevertheless 
impressed  upon  Galvani  the  belief  that  the  two  distinct  phenomena 
were  due  to  one  and  the  same  cause,  namely :  that  of  electricity,  and 
he  described  his  discovery  of  what  he  styled  "animal  electricity" 
in  his  celebrated  memoir,  "De  Viribus  Electricitatis,"  in  1791. 
A  complete  history  of  the  voltaic  cell  and  its  origin  would  debar 
us,  for  lack  of  space  available  here,  from  considering,  as  we  must, 
the  later  theories  and  the  more  experimental  and  practical  side  of 
the  electric  battery.  To  give  an  idea,  however,  of  the  hopeless 
state  of  affairs  existing  until  the  theory  of  electrolytic  dissociation 
threw  some  light  upon  the  subject,  we  will  refer  to  the  views  of  Stur- 
geon who,  writing  on  the  subject  of  Voltaism  in  1842,  expressed  himself 
as  follows:  "  Voltaism  is  the  production  of  electricity  by  the  associa- 
tion of  metals  and  other  inorganic  bodies  by  the  simple  contact  of 
inorganic  bodies,  whether  solid  or  fluid."  Galvanism  is  the  produc- 
tion of  electrical  currents,  "  either  by  a  natural  or  artificial  associa- 
tion of  animal  matter,  whether  alive  or  dead."  The  "  animal 
matter  "  element  of  this  definition  was  eventually  abandoned  by  most 
of  the  investigators,  when  two  distinct  theories  were  formulated, 
namely:  "The  contact  theory  of  the  cell "  and  the  "chemical  theory 
of  the  cell."  De  la  Rive,  writing  in  1853,  defined  the  voltaic  cell  in 
the  following  words :  "An  apparatus  in  which  electricity  is  developed, 
according  to  some,  by  the  contact  of  two  metals  of  a  different  nature, 
and  according  to  others,  by  the  chemical  action  of  the  liquids  with 
which  it  is  charged  upon  one  of  the  two  metals  which  enter  into  its 
formation."  Faraday  expressed  himself  upon  these  two  theories  of 
the  cell  as  follows:  "The  contact  theory  assumes  that  when  two 
different  bodies  being  conductors  of  electricity  are  in  contact,  there 
is  a  force  at  the  point  of  contact  by  which  one  of  the  bodies  gives  a 


THE  PRIMARY   CELL. 


221 


part  of  its  natural  portion  of  electricity  to  the  other  body,  which  the 
latter  takes  in  addition  to  its  own  natural  portion;  that,  though 
the  touching  points  have  thus  respectively  given  and  taken  electricity 
they  cannot  retain  the  charge  which  their  contact  has  caused,  but 
discharge  their  electricities  to  the  masses  respectively  behind  them; 
that  the  force  which  at  the  point  of  contact  induces  the  particles 
to  assume  a  new  state  cannot  enable  them  to  keep  that  state;  that 
all  this  happens  without  any  permanent  alteration  of  the  parts  that 
are  in  contact,  and  has  no  reference  to  their  chemical  forces." 

"The  chemical  theory  assumes  that  at  the  place  of  action,  the 
particles  which  are  in  contact,  act  chemically  upon  each  other  and 
are  able,  under  the  circumstances,  to  throw  more  or  less  of  the  acting 
force;  that,  in  the  most  favorable  circumstances,  the  whole  is  con- 
verted into  dynamic  force;  that  then  the  amount  of  current  force 
produced  is  an  exact  equivalent  of  the  original  force  employed 
and  that  in  no  case  can  any  electric  current  be  produced  without 
the  active  exertion  and  consumption  of  an  equal  amount  of  chem- 
ical force  ending  in  a  given  amount  of  chemical  change." 

Gore  writes  upon  the  theory  of  the  cell  as  follows:  "The  essential 
cause  is  the  stored-up  and  ceaseless  molecular  energy  of  the  corroded 
metal  and  of  the  corroding  element  of  liquid  with  which  it  unites, 
whilst  contact  is  only  a  static  condition,  and  chemical  action  is  the 
process  or  mode  by  which  the  molecular  motions  of  those  substances 
are  more  or  less  transformed  into  heat  and  current." 

So  much  for  these  old  theories.  What  have  they  taught  us? 
Can  we,  in  the  light  of  them,  satisfactorily  explain  the  cause  of  the 
electric  current,  its  origin,  or  birth?  What  must  we  do  in  order 
to  produce  the  electrical  current  by  chemical  action?  In  the  light 
of  our  chemical  knowledge,  let  us  see  what  takes  place  in  the  pro- 
duction of  electricity  in  the  following  simple  experiment:  A  little 
dilute  sulphuric  acid  is  placed  in  a  beaker  glass  and  two  strips  of  metal 
of  dissimilar  character,  for  example,  platinum  and  zinc,  are  partly  im- 
mersed in  the  liquid  so  that  they  do  not  touch  each  other.  If  now  the 
uppermost  ends  of  these  metal  strips  be  joined  by  a  suitable  wire,  an 
electric  current  in  the  direction  from  the  platinum  to  the  zinc  will 
be  produced,  as  may  be  proven  by  a  magnetic  needle  or  galvanometer. 
Bubbles  of  hydrogen  may  be  seen  to  make  their  appearance  on  the 
surface  of  the  immersed  platinum  strip.  So  much  for  the  physical 


222  EXPERIMENTAL  ELECTROCHEMISTRY. 

manifestation.  What  can  we  say  of  the  chemical?  As  general 
chemists,  we  can  merely  analyze  the  solution  and  weigh  the  metal 
strips  for  information  relative  to  their  loss  or  increase  in  weight.  If  we 
analyze  the  diluted  sulphuric  acid  solution  we  will  find  that  it  is  no 
longer  merely  a  sulphuric  acid  solution,  but  that  we  also  have  zinc 
sulphate  present,  and  that  the  strip  of  zinc  has  lost  in  weight,  whereas 
the  platinum  is  unaltered.  An  electric  current  has  been  produced. 
What  was  its  origin  and  how  can  we,  as  physical  chemists,  explain  its 
production?  Before  the  advancement  of  the  theory  of  electrolytic 
dissociation  this  was  a  matter  veiled  in  great  obscurity.  We  could,  of 
course,  say  that  the  electric  current  was  the  result  of  chemical  action, 
or  that  it  accompanied  the  formation  of  sulphate  of  zinc,  or  that  it 
was  produced  when  zinc  was  dissolved  in  sulphuric  acid,  but  does  this 
really  take  us  as  deeply  into  the  inquiry  as  we  wish  to  go  ?  In  order 
to  comprehend  the  modern  theory  of  the  cell,  as  based  on  the  theory 
of  electrolytic  dissociation,  we  must  know  something  concerning  the 
solution  tension  of  metals  in  addition  to  facts  in  connection  with  the 
theory  of  electrolytic  dissociation.  The  solution  tension  of  metals 
when  immersed  in  liquids  may  be  compared  with  the  vapor  tension 
of  liquids.  When  a  bar  of  metal  is  immersed  in  a  liquid  it  tends 
to  dissolve,  and  does  dissolve  to  a  greater  or  less  extent.  When,  on 
the  other  hand,  for  example,  an  open  vessel  containing  a  liquid  is 
placed  in  the  laboratory,  the  liquid  tends  to  evaporate  and  does 
evaporate  to  a  greater  or  less  extent.  A  bar  of  common  zinc  will 
dissolve  in  dilute  sulphuric  acid  much  more  rapidly  than  a  bar  of 
iron,  and,  on  the  other  hand,  an  open  vessel  of  ether  will  evaporate 
much  more  rapidly  than  a  similar  vessel  of  water.  We  may  term 
the  tendency  of  the  zinc  to  go  into  solution,  the  solution  tension 
of  zinc,  and  the  tendency  of  iron  to  go  into  solution,  the  solution 
tension  of  iron,  and  from  the  fact  that  they  go  into  solution  at 
different  rates,  we  may  logically  deduce  that  they  have  different  ten- 
dencies to  go  into  solution,  or,  in  other  words,  we  may  say  that  they 
have  different  solution  tensions.  We  will,  a  little  later  in  this 
chapter,  take  up  the  experimental  determination  of  the  solution 
tension  of  metals.  We  will  see,  when  we  come  to  this  work,  that 
we  have  means  for  quantitively  measuring  and  comparing  what  we 
now  term  the  solution  tensions  of  the  metals.  We  can  at  a  fixed 
temperature  establish  a  solution  tension  value  for  any  metal  in 


THE  PRIMARY  CELL. 


a  given  liquid,  as  we  can  measure  the  vapor  pressure  or  tendency  of 
a  liquid  to  volatilize  at  a  given  temperature.  A  most  important 
fact  for  us  to  take  into  account  at  this  time  is  the  fact  that  the  solu- 
tion tension  of  any  metal  immersed  in  any  given  liquid  is  indepen- 


FlG.  Top. — Experiment  to  show  that  Solution  Tension  is  Independent  of  Surface  Area. 

dent  of  the  size  of  surface  of  the  metal  immersed,  which,  we  will  see 
is  the  case  as  indicated  by  E.M.F.  phenomena,  if  we  perform  an 
experiment  as  indicated  in  Fig.  109.  We  know,  and  can  experi- 
mentally demonstrate  that  the  vapor  pre:sure  of  ether,  for  example, 
is  independent  of  the  surface  exposed  under  the  same  conditions 
of  temperature  and  barometric  pressure.  For  experiment  with 
vapor  tensions  the  reader  is  referred  to  any  good  text-book  on 


224  EXPERIMENTAL  ELECTROCHEMISTRY. 

experimental  physics.  As  we  will  presently  see,  we  may  arrange 
the  known  metals  in  a  series,  in  the  order  of  their  solution  tensions, 
and  such  a  table  of  the  metals  may  be  referred  to  in  reference  to 
a  liquid  or  electrolyte  as  the  tension  series  of  the  metals.  This 
preliminary  outline  has  been  necessary,  in  the  opinion  of  the  writer, 
before  presenting  to  the  student  the  following  experiment,  which, 
upon  the  basis  of  the  theory  of  electrolytic  dissociation,  explains 
in  a  beautiful  and  satisfactory  manner  the  origin  of  the  electric 
current  in  the  voltaic  cell. 

The  experiment  to  which  we  now  refer  has  been  styled  by 
Ostwald  and  others,  "Chemical  Action  at  a  Distance."  Ostwald 
presented  a  paper  in  1891  entitled,  "Chemische  Fernewirkung." 
An  exceedingly  interesting  point  to  which  Ostwald  draws  atten- 
tion is  the  fact  that  amalgamated  zinc  is  not  dissolved  by  dilute 
acids.  It  has  also  been  pointed  out  that  chemically  pure  zinc 
will  not  dissolve  in  dilute  acids.  This  will  appear  to  those 
familiar  only  with  general  chemistry  to  be  a  remarkable  statement. 
The  general  chemist,  without  a  knowledge  of  physical  chemistry, 
will  find  it  difficult  to  believe  that  sulphuric  acid,  for  example,  will 
not  dissolve  a  stick  of  zinc  if  the  latter  be  chemically  pure.  If,  on 
the  other  hand,  the  zinc  is  impure,  that  is  to  say,  contains  traces 
of  other  metal  as  alloy  or  other  metals  adhering  or  cast  within  or 
upon  its  surface,  the  zinc  will  dissolve  with  rapidity.  It  is  quite 
well  known  in  this  connection,  that  in  the  preparation  of  hydrogen 
by  throwing  granulated  zinc  in  dilute  sulphuric  acid  that  the  evo- 
lution of  the  gas  is  greatly  promoted  by  the  addition  of  some  scrap 
platinum  or  a  few  bright  iron  nails.  Ostwald,  in  his  writing  con- 
cerning this  very  point,  speaks  first  of  wrapping  a  platinum  wire 
around  the  top  of  a  rod  of  zinc  and  immersing  its  lower  end  in 
dilute  acid.  If  the  rod  of  zinc  is  chemically  pure  there  will  be 
no  appreciable  chemical  action  if  the  free  end  of  the  platinum 
wire  does  not  dip  in  the  acid.  If,  however,  the  end  of  this  platinum 
wire  is  immersed  in  the  acid,  the  zinc  will  go  into  solution  rapidly, 
and  hydrogen  will  be  liberated  from  the  immersed  end  of  the  plati- 
num wire.  Ostwald  also  states  that  it  is  not  necessary  for  the  zinc 
to  be  surrounded  by  the  platinum  wire,  for  if  such  a  wire  touches 
the  zinc  at  any  point  where  it  is  immersed  in  the  acid,  solution 
will  take  place.  It  was  also  suggested  that  the  zinc  and  platinum 


THE  PRIMARY   CELL. 


225 


wire  be  joined  at  one  place  and  then  the  free  lower  ends  of  both 
zinc  and  platinum  be  immersed  in  a  vessel  containing,  for  example, 
potassium  sulphate.  A  porous  partition  is  placed  between  the 
immersed  zinc  and  the  platinum  so  that  the  electrolyte  around  the 
zinc  is  separated  from  the  electrolyte  around  the  platinum. 
Ostwald  then  asked  the  following  question:  "To  which  metal  must 
we  add  sulphuric  acid  in  order  that  the  zinc  may  be  dissolved?" 
This  question,  to  the  general  chemist  without  a  knowledge  of 
certain  fundamental  principles  of  electrochemistry,  would  appear 
to  be  an  absurd  one,  for  it  would  seem  to  him  to  be  very  evident 
that  the  acid  should  be  poured  into  the  partition  containing  the 
zinc.  If  such  an  experiment  is  carried  out  we  will  find  that  in 
order  to  secure  the  solution  of  the  zinc,  strange  as  it  may  appear, 
the  acid  must  be  added  to  the  compartment  containing  the  platinum. 
When  the  zinc  dissolves,  a  brisk  liberation  of  hydrogen  gas  is 
observed  from  the  platinum.  This  experiment  is  illustrated  in 
Fig.  no  and  consists  of  two  beaker  glasses  containing  a  solution  of 

X: 


FIG.  no.— Experiment  to  Show  '•  Chemical  Action  at  a  Distance." 


potassium  sulphate,  joined  together  by  a  siphon-tube  containing 
some  of  the  same  solution.  In  the  left  of  our  illustration  may  be  seen 
a  cell  of  glass,  cylindrical  in  shape,  on  the  pattern  of  an  ordinary 
lamp-chimney,  its  upper  end  being  fitted  with  a  perforated  stopper, 
as  shown,  carrying  a  rod  of  pure  zinc.  The  lower  end  of  this 
cylinder  is  tightly  closed  with  vegetable  parchment,  simply  to  act 
as  a  porous  diaphragm.  In  the  present  arrangement  of  two  beakers 


226  EXPERIMENTAL   ELECTROCHEMISTRY. 

separated  by  a  siphon-tube  this  precaution  to  prevent  diffusion 
currents  is  not  absolutely  necessary.  The  glass  cylinder  carrying 
the  zinc  is,  of  course,  also  filled  with  the  solution  of  potassium  sul- 
phate. A  piece  of  platinum  wire  is  wrapped  around  the  top  of  the 
zinc  bar,  and  a  second  piece,  terminating  in  a  spiral  to  give  it  more 
surface,  is  immersed  in  the  distant  beaker.  If  now  a  few  drops  of 
sulphuric  acid  be  introduced  within  the  cylindrical  cell  containing 
the  zinc,  there  will  be  practically  no  solution  of  the  metal.  If,  on 
the  other  hand,  a  few  drops  of  sulphuric  acid  are  poured  into  the 
beaker  at  a  distance,  and  connected  by  the  siphon  containing  the 
platinum  coil,  a  brisk  evolution  of  hydrogen  will  take  place  from  this 
platinum  wire,  and  after  a  few  minutes  the  presence  of  zinc  sulphate 
within  the  glass  cylinder  surrounding  the  rod  of  zinc  may  be  proven 
by  analytical  means.  In  the  drawing  one  will  observe  an 
arrow  pointing  toward  the  rod  of  zinc  in  the  left-hand  beaker,  and 
just  above  the  arrow  the  platinum  wires  are  shown  in  contact.  If 
after  adding  sulphuric  acid  to  the  right-hand  beaker,  as  shown  in 
the  drawing,  the  liberation  of  hydrogen  from  the  platinum  spiral 
and  solution  of  zinc  in  the  left  beaker  is  noted,  we  separate  these 
platinum  wires  from  contact,  the  liberation  of  hydrogen  ceases 
together  with  the  solution  of  zinc.  Upon  touching  the  platinum 
wires  together  again,  however,  the  chemical  action  recommences, 
and  if  we  bring  a  sensitive  magnetic  needle  in  the  neighborhood 
of  the  platinum  wire  we  will  find  that  an  electric  current  is  flow- 
ing through  it  in  the  direction  of  the  arrow,  namely :  from  the  right- 
hand  beaker  containing  the  platinum  to  the  left-hand  beaker  con- 
taining the  zinc. 

The  explanation  of  these  phenomena  is  comparatively  simple 
when  based  upon  the  theory  of  electrolytic  dissociation.  The 
source  of  the  current  in  a  voltaic  cell  may  be,  therefore,  understood 
from  the  following  consideration :  When  a  rod  of  zinc  is  immersed 
in  a  solution  of  a  neutral  salt,  potassium  sulphate  for  example, 
zinc  ions  are  sent  off  in  solution  because  of  the  solution  tension  of 
the  zinc.  These  zinc  ions  are  driven  into  solution  because  of  the 
solution  tension  of  zinc  in  an  analogous  manner  to  the  sending 
off  of  ether  molecules  into  the  air  when  an  open  vessel  of  ether  is 
allowed  to  stand  in  the  laboratory.  In  the  case  of  the  immersed 
zinc  it  is  made  negative  in  electrical  sign,  and  the  solution  which 


THE   PRIMARY  CELL.  227 

has  received  the  ions,  which  are  positive  in  sign,  becomes  itself  posi- 
tive. Thus  solution  continues  until  a  difference  of  potential  in 
solution  is  established.  Again  comparing  the  phenomena  of  vapor 
tension;  ether  in  an  open  vessel  would  continue  to  evaporate  until 
an  equilibrium  is  established.  In  the  case  of  the  zinc  rod  immersed 
in  the  sodium  sulphate  solution,  the  number  of  zinc  ions  driven 
off,  although  very  small,  establish  an  equilibrium  after  a  while. 
Referring  once  more  to  the  case  of  the  zinc  rod  in  the  electrolyte, 
the  driving  off  of  the  zinc  ions  will  cease  after  a  certain  point  has 
been  obtained,  because  of  an  excess  of  positive  ions  in  the  solution. 
In  order  that  more  of  the  zinc  ions  may  be  driven  out  some  of  these 
positive  ions  must  be  removed.  If  the  zinc  is  connected  with 
another  metal,  for  example  our  platinum  wire,  such  platinum  wire, 
of  course,  takes  the  same  negative  charge  as  the  zinc.  When  the 
negative  end  of  this  platinum  wire,  therefore,  is  coiled  and  immersed 
in  the  solution  it  attracts  the  excess  positive  zinc  ions  which  exist 
in  the  solution.  We  might  expect,  from  the  description  of  the 
experiment  as  far  as  we  have  gone,  that  the  zinc  ions  in  the  solu- 
tion would  be  attracted  to  the  platinum  spiral,  give  up  their  charges 
and  deposit  thereon,  or,  in  the  case  of  potassium,  decompose  the 
water  which  is  present  with  the  liberation  of  hydrogen.  The  be- 
havior in  such  a  state  of  affairs  depends  upon,  not  only  the  nature 
of  the  ion,  but  of  the  electrode  also.  In  such  an  experiment,  with 
the  positive  ion,  which  is  the  potassium  resulting  from  potassium 
sulphate,  the  difference  in  potential  produced  upon  the  introduc- 
tion of  the  zinc  is  insufficient  to  cause  the  potassium  ion  to  give 
up  its  charge  to  the  platinum.  If,  however,  a  little  sulphuric  acid 
is  added  to  the  beaker  at  the  right  containing  the  platinum  coil, 
and  the  wires  are  in  contact,  the  difference  in  potential  produced  by 
introducing  the  bar  of  zinc  is  sufficient  to  compel  the  hydrogen 
to  give  up  its  positive  charge  to  the  platinum  spiral  and  appear  upon 
its  surface  as  minute  bubbles.  The  hydrogen  ions  in  their  becom- 
ing hydrogen  atoms  give  up  positive  electricity  to  the  platinum, 
neutralizing  the  negative  charge  which  the  latter  carries.  A  current 
of  electricity  will  then  flow  along  the  wire  in  the  direction  of  the 
arrow,  as  indicated,  to  the  zinc,  which  will,  of  course,  become  less 
negative  than  before  the  hydrogen  separated  at  the  platinum  spiral, 
and  the  difference  in  potential  between  the  zinc  rod  and  the  sur- 


228  EXPERIMENTAL   ELECTROCHEMISTRY. 

rounding  solution  becomes  less.  More  zinc  will,  therefore,  dissolve 
or  be  driven  into  solution  as  zinc  ions.  Additional  hydrogen  ions 
give  up  other  charges  to  the  platinum  spiral  and  separate  as  gas, 
which,  of  course,  in  turn  tends  to  make  the  zinc  still  less  negative. 
Now,  as  long  as  we  have  the  circuit  closed,  we  will  have  an  electric 
current,  one  from  the  platinum  to  the  zinc  as  a  result  of  the  con- 
version of  positive  hydrogen  ions  to  the  ordinary  hydrogen  atoms. 
We  have  already  referred  to  the  fact  that  pure  zinc  does  not  dissolve 
in  acids,  while  zinc  which  is  impure  displaces  the  hydrogen  of  an 
acid  with  readiness,  or,  as  we  may  say  in  popular  language,  dissolves. 
The  tendency  of  zinc,  whether  pure  or  impure,  to  go  into  solution 
is  the  same,  only  in  one  case  it  does  and  the  other  case  it  does  not. 
Pure  zinc,  however,  dissolves  readily  in  an  acid,  or  as  we  may  say, 
technically  speaking,  displaces  the  hydrogen  in  an  acid  with  avidity 
when  in  contact  with  some  other  metal  of  lower  solution  tension, 
such  as  platinum  for  example,  immersed  in  the  acid.  The  differ- 
ence is  not  in  the  solution  of  the  zinc,  but  is  due  to  the  ease  with 
which  hydrogen  may  escape  from  the  solution.  The  presence  of 
such  a  metal  as  platinum  with  a  very  low  solution ,  tension,  allows 
the  hydrogen  to  escape  from  its  surface  with  ease,  and  upon  this 
principle  we  may  see  why  impure  zinc  dissolves  in  acids,  when 
such  impurities  of  low  solution  tension  exist  and  act  as  points,  or 
surfaces  from  which  the  hydrogen  ions  may  discharge  their  elec- 
tricity and  escape  as  hydrogen  gas.  With  a  stick  of  impure  zinc 
we  have  numerous  impurities  in  the  way  of  specks  upon  its  surface 
of  a  lower  solution  tension  than  the  zinc  itself,  and  we  will  have 
a  multiplicity  of  little  galvanic  circuits  between  the  zinc  impuri- 
ties and  through  the  electrolyte  from  the  impurities  to  the  zinc 
through  the  point  of  metallic  contact.  The  reason  why  chemically 
pure  zinc  will  not  dissolve  may  also  be  ascribed  to  the  fact  that  this 
metal  itself  has  very  high  solution  tension  and  sends  its  own  positively 
charged  ions  into  solution  under  a  high  solution  tension  opposing 
the  tension  of  any  other  positive  ions,  like  hydrogen  for  example, 
upon  it.  The  rod  of  pure  zinc  will  not  dissolve  in  acids,  therefore, 
because  the  hydrogen  ions  cannot  give  up  their  positive  charges  to 
it  to  escape  as  hydrogen  molecules.  As  we  saw  by  referring  to 
Fig.  109,  electromotive  force  is  an  exponent  of  solution  tension, 
and  from  the  experiment  as  depicted  it  may  be  seen  that  this  solu- 


THE  PRIMARY  CELL.  229 

tion  tension  is  independent  of  the  size  or  area  of  the  metals  immersed 
in  an  electrolyte.  A  difference  in  potential  between  the  metal  and 
the  electrolyte  is  therefore  established,  which  proves  to  be  the  fun- 
damental origin  of  the  E.M.F.,  produced  in  any  given  combination. 
We  may  ascribe  the  direct  cause  of  this  difference  of  potential 
to  the  solution  tension  of  the  metal  which  tends  to  drive  ions 
from  the  metal  into  solution,  making  the  metal  itself  negative  in 
sign  and  the  solution  positive  in  sign,  because  of  the  presence  of  posi- 
tively charged  ions.  It  may  be  pointed  out  here  that  we  also  have 
a  pressure  in  such  a  cell  antagonistic  to  the  solution  tension  of  the 
metal,  and  this  is  the  osmotic  pressure  of  the  solution  itself,  which 
tends  to  cause  the  ions  driven  out  to  separate  on  the  electrode  in 
the  metallic  condition.  As  a  consequence  of  these  opposing  forces 
we  have  the  formation  of  a  double  layer  so  to  speak,  and  the  dif- 
ference in  potential  between  the  metal  and  the  solution.  This 
double-layer  phenomenon  is  referred  to  in  the  electrochemical  works 
as  a  Helmholtz  double  layer.  Dr.  Nernst  very  clearly  describes 
the  phenomena  of  the  Helmholtz  double  layer  in  such  a  concise 
and  lucid  manner  that  it  is  deemed  of  value  to  the  student  to  trans- 
late his  own  words  upon  the  subject  here.  "Let  us  now  consider 
what  will  take  place  if  we  dip  a  metal  whose  electrolytic  solution 
tension  is  P  into  a  solution  of  one  of  its  salts;  the  osmotic  pressure 
of  the  metal  ions  in  this  solution  being  p.  Let  at  first  P  >  p,  at  the 
moment  of  contact  a  number  of  positively  charged  metallic  ions, 
driven  by  this  large  pressure,  will  pass  into  solution.  Since  by  the 
latter  a  certain  amount  of  positive  electricity  is  carried  from  the 
metal  into  the  solution,  the  liquid  receives  a  positive  charge,  which 
arranges  itself  in  the  form  of  the  positive  ions  contained  in  the 
solution  on  the  surface  of  the  metal.  At  the  same  time  there  is,  of 
course,  a  corresponding  amount  of  negative  electricity  set  free  in 
the  metal,  which  also  passes  to  the  surface  of  the  metal.  We  recog- 
nize at  once  that  at  the  surface  of  contact  of  metal  and  electrolyte 
the  two  kinds  of  electricity  must  accumulate  in  the  form  of  a  double 
layer,  whose  existence,  as  is  well  known,  was  made  probable  some 
time  ago  by  Von  Helmholtz  in  an  entirely  different  way. 

"This  double  layer  furnishes  one  component  of  force,  which 
acts  at  right  angles  to  the  surface  of  contact  of  the  metal  and  the 
electrolyte,  and  which  tends  to  drive  the  metallic  ions  from  the 


230  EXPERIMENTAL   ELECTROCHEMISTRY. 

electrolyte  on  to  the  metal,  and  thus  acts  in  opposition  to  the  solu- 
tion tension.  Equilibrium  will  be,  of  course,  established  when  these 
two  forces  equalize  one  another.  The  final  result  will  be  the  appear- 
ance of  an  electromotive  force  between  the  metal  and  the  electro- 
lyte, which  will  give  rise  to  a  galvanic  current  from  the  metal  to  the 
liquid,  if  by  any  device  its  existence  is  made  possible. 

"IfP<p  the  reverse  of  course  takes  place.  Metallic  ions  separate 
from  the  electrolyte  and  are  precipitated  on  to  the  metal  until  the 
electrostatic  component  of  force  of  the  positive  charge  of  the  metal 
and  the  negative. charge  of  the  liquid  thus  produced  are  in  equilibrium 
with  the  excess  of  osmotic  pressure.  An  electromotive  force  again 
appears  between  the  metal  and  the  electrolyte,  which,  under  suitable 
conditions,  gives  rise  to  a  galvanic  current,  but  in  this  case  opposite 
in  direction  to  the  case  first  considered. 

"If,  finally,  P  =  p  the  metal  and  electrolyte  are  in  equilibrium 
at  the  first  moment  of  contact;  therefore,  no  difference  in  potential 
exists  between  the  two." 

In  our  practical  and  experimental  work  it  is  very  important  that 
we  note  quantitatively  the  potential  differences  existing  between 
metals  and  solutions,  and  in  order  to  practically  determine  this 
we  will  adopt  the  method  involving  a  "normal  electrode."  This 
method  employs  the  use  of  a  previously  prepared  electrode,  which 
has  been  termed  a  normal  electrode,  because  its  potential  is  known. 
This  normal  electrode  is  connected  with  a  metal  whose  difference 
in  potential  we  wish  to  ascertain  and  the  E.M.F.  of  the  entire 
system  determined.  As  we  know  the  potential  of  the  normal  elec- 
trode, that  of  the  metal  under  examination  is  easily  determined, 
the  E.M.F.  of  the  two  when  properly  combined  being  the  difference 
between  the  potentials  on  the  two  sides.  The  use  of  the  normal 
electrode  may  be  understood  by  referring  to  Fig.  in,  where  at  the 
extreme  left  we  have  the  normal  electrode  equipment,  the  beaker 
glass  in  the  center  containing  the  metal  x,  whose  tension  we  are 
.-about  to  study,  while  at  the  right  we  have  a  sensitive  standard 
Tolt-meter.  The  normal  electrode  equipment  consists  of  a  wide- 
mouth  glass  bottle  containing  a  layer  of  purified  mercury  in  the 
bottom,  as  indicated.  On  top  of  the  mercury  a  layer  of  mercurous 
chloride  is  placed,  and  on  top  of  this  a  normal  solution  of  potassium 
chloride  is  poured.  A  platinum  wire  which  passes  through  a  pro- 


THE  PRIMARY   CELL. 


231 


tecting  glass  tube  is  suspended  from  the  stopper,  as  shown.    The 
wire  is  sealed  in  a  glass  tube  in  such  a  way  that  its  lower  extremity, 


which  is  in  the  form  of  a  tiny  coil,  comes  into  contact  with  the  metallic 
mercury  in  the  bottom  of  the  bottle.     A  siphon-tube  passes  through 


232 


EXPERIMENTAL  ELECTROCHEMISTRY. 


a  second  hole  in  the  stopper  of  this  bottle  and  dips  in  the  normal 
potassium  chloride  solution,  after  having  itself  been  filled  with  the 
same  electrolyte.  Connection  is  made  with  the  mercury  through 
the  platinum  wire,  insulated  by  the  glass  tube,  and  this  mercury 
serves  as  one  electrode.  The  siphon  is  inserted  in  the  liquid,  whose 


FIG.  112. — Special  and  Convenient  Design  of  Normal  Electrode. 


potential  against  the  metal  under  examination  we  wish  to  learn. 
The  metal  in  question  serves  as  the  other  electrode  and  is  connected 
up  with  a  sensitive  volt-meter,  as  shown,  and  the  E.M.F.  of  the  entire 
system  determined.  The  electromotive  force  between  the  mercury 
and  the  potassium  chloride  is  .56  volt  at  the  ordinary  temperature 
of  the  laboratory.  This  .56  volt  may  be  used  as  a  constant  for  our 


THE  PRIMARY  CELL 


233 


normal  electrode,  no  matter  what  its  size,  if  put  together  with  chemi- 
cally pure  materials  upon  the  plan  as  indicated.  If  the  liquid  in 
the  beaker  containing  the  metal,  whose  tension  is  to  be  measured, 
reacts  chemically  with  potassium  chloride,  the  solution  of  some 
indifferent  compound  may  be  interposed  between  the  two.  Fig.  112 
shows  a  very  neat  and  convenient  design  for  a  normal  electrode. 
Here  we  have  a  glass  vessel  containing  a  platinum  wire  fused  into 
its  lower  end  to  make  contact  with  the  mercury.  The  mercurous 
chloride  is  then  put  in  position,  as  in  the  previous  case,  and  the 
normal  potassium  chloride  solution  put  on  top  and  made  to  fill  the 
siphon,  which  in  this  instance  is  fused  into  the  side  of  the  vessel. 
This  form  of  normal  electrode  is  conveniently  held  in  an  iron  retort 
clamp  as  shown. 

The  following  table  is  taken  from  the  work  of  Neumann  and 
represents  the  differences  of  potential  between  several  metals  and 
normal  solutions  of  their  salts. 


Metal.  Chloride. 

Magnesium i .  231  Volts. 

Aluminium 1-015  " 

Zinc 0.503  " 

Cadmium 0.174  " 

Iron 0.087  " 

Cobalt -0.015  " 

Nickel —0.020  " 

Tin -0.085  " 

Lead —0.095  " 

Gold -i-356  " 

Platinum — 1.066  " 

We  have  learned  that  the  solution  tension  of  a  metal  is  respon 
sible  for  the  difference  in  potential  between  itself  and  the  electro- 
lyte into  which  it  is  immersed.  If  we  determine  the  potential  differ- 
ence and  the  value  of  the  osmotic  pressure  of  the  positive  ions  in 
solution,  we  have  the  data  necessary  for  calculating  the  solution 
tension  of  the  metal. 

A  few  common  metals  arranged  in  the    order  of  their  solution 
tension  is  given  below,   and  this  may  be  termed  a  tension  series. 


234  EXPERIMENTAL  ELECTROCHEMISTRY. 

Magnesium, 

Zinc, 

Aluminum, 

Cadmium, 

Iron, 

Cobalt, 

Nickel, 

Lead, 

Mercury, 

Silver, 

Copper. 

A  metal  anywhere  in  the  above  series  will  tend  to  precipitate 
from  its  salt  a  metal  located  lower  in  the  series,  for  example,  zinc 
will  precipitate  copper  from  its  salts,  etc.  A  metal  at  any  point 
in  the  series,  when  made  an  electrode  in  a  cell  of  battery  against  a 
metal  lower  in  the  series,  serving  as  the  other  electrode,  will  throw 
off  ions  in  the  solution,  and  thereby  become  the  negative  pole.  Zinc 
is  the  negative  pole  in  almost  all  cells  of  battery.  The  position 
of  a  -metal  in  the  tension  series  is  of  extreme  interest  to  us  in  the 
design  of  primary  batteries. 

We  will  close  the  present  chapter  by  a  consideration  of  the 
energy  of  the  primary  cell  based  upon  a  known  chemical  reaction. 
If  we  know  the  chemistry  of  a  cell  of  battery  we  can,  by  a  simple 
mathematical  process,  predict  what  its  electromotive  force  will  be. 
This  calculation  may  be  very  simple  or  very  complex,  depending 
upon  which  way  we  attack  the  problem.  As  it  has  been  the  aim 
of  the  author  to  avoid  the  higher  mathematics  in  the  present  work, 
we  will  proceed  with  a  comparatively  simple  formula.  Let  us, 
therefore,  select  a  typical  simple  cell,  look  into  its  chemistry, 
and  predict  therefrom  the  maximum  electromotive  force  which 
such  a  cell  is  capable  of  giving.  This  work  will  take  us  back  into 
certain  of  our  fundamental  principles  as  introduced  in  the  early 
portion  of  the  present  book  and  involve  Faraday's  Law,  together 
with  several  fundamental  units,  and  the  most  important  constant 
96,540.  For  this  purpose  of  illustration  we  may  do  best  by  select- 
ing the  well-known  Daniell  type  of  element,  or  cell.  Helmholtz  has 
pointed  out  that  a  relationship  may  be  established  between  the  energy 


THE  PRIMARY  CELL.  235 

of  the  chemical  process,  or,  in  other  words,  the  chemical  energy  of 
a  cell,  and  the  electrical  energy  produced  in  exchange.  It  will  be 
seen  that  under  ordinary  conditions,  most  of  the  energy  which  could 
be  obtained  as  the  heat  of  chemical  action  can  be  converted  into 
electrical  energy  and  be  made  to  do  work  as  an  electric  current. 
If  we  allow  Q  to  represent  the  available  heat  energy,  for  one  gram- 
equivalent  of  a  compound  that  enters  into  chemical  combination 
in  a  cell,  it  may  be  assumed  in  some  cases  that  an  amount  of  elec- 
trical energy  equivalent  to  this  heat  energy  can  be  obtained  from 
the  cell  for  each  gram -equivalent  of  chemical  transfer.  In  the  case 
of  a  Daniell  cell,  the  conditions  may  be  represented  by  the  following 
equation : 

Cu,  CuSO4  Solution;  ZnSC>4  Solution  Zn. 

After  the  cell  has  been  allowed  to  do  work,  the  condition  of  affairs 
may  be  represented  as  follows: 

Zn,  CuSO4=Cu,  ZnSO4. 

Zinc  is  therefore  dissolved  at  one  pole  of  the  battery,  and  copper 
is  deposited  at  the  other.  The  heat  value  of  such  a  reaction  is 
the  difference  between  the  heat  of  formation  of  copper  sulphate  and 
zinc  sulphate  in  aqueous  solution.  We  have,  therefore,  106,090  — 
55,960  =  50,130  calories  per  gram-equivalent.  When  32.5  grams 
of  metallic  zinc  displace  an  equivalent  of  metallic  copper  from  a 
solution  of  sulphate  of  copper,  25,065  calories  are  set  free.  We 
will  remember  from  our  study  of  Faraday's  Law  that  about  96,500 
coulombs  of  electricity  are  obtained  for  every  32.5  grams  of  zinc 
transported,  so  if  this  displacement  takes  place  in  a  suitable  cell 
we  will  have  96,500  coulombs  of  electricity  delivered  to  us.  We 
also  learned  that  the  Joule,  which  is  the  product  of  i  volt  by  i  cou- 
lomb, is  equal  to  .00024  large  Calories  or  .24  small  calories.  The 
electrical  energy  equal  to  this  number  of  heat  units  is  25,065  -^-.24  = 

104,240  Joules,  therefore  —7 — —~  =  1.08  volts.    This  calculation  is 

quite  similar  in  character  to  the  method  introduced  when  we  were 
calculating  the  minimum  E.M.F.  required  to  decompose  the  gram- 
molecular  weight  of  any  electrolyte  when  its  heat  of  formation  is., 
known.    The  Daniell  cell,  therefore,    should  give  us  an  E.M.F.  of 


236  EXPERIMENTAL  ELECTROCHEMISTRY. 

1.08  volts;  and  direct  measurement  of  this  cell  gives  us  1.09  to  i.i 
volts.  It  will,  therefore,  be  seen  how  close  we  may  come  to 
the  prediction  of  E.M.F.  of  a  cell  when  we  know  its  general 
chemistry. 


CHAPTER  XVII. 
THE  SECONDARY  CELL. 

THE  secondary  cell  in  many  ways  is  immensely  superior  to  all  forms 
of  primary  battery  and  is  of  the  utmost  interest  to  electrochemists. 
Unlike  the  primary  cell,  it  is  not  susceptible  to  polarization,  or 
counteraction,  resulting  from  the  formation  of  a  film  of  hydrogen 
gas  upon  the  surface  of  the  negative  electrode.  As  hydrogen  is 
negative  to  zinc,  for  example,  a  counter  electromotive  force  is  set 
up  and  the  conditions  very  materially  modify  the  output  in  the 
externa1  circuit.  Efforts  have  been  made  to  diminish  this  in  the 
primary  cell  by  adding  depolarizers,  which  substances  combine 
with  the  hydrogen  liberated  at  the  cathode  to  form  water  and  are, 
therefore,  oxidizing  agents;  bichromate  of  potash  is  frequently  used 
for  this  purpose.  Whereas  the  chemistry  of  the  primary  cell  is  well 
known,  that  of  the  secondary  cell  or  storage  battery  using  lead 
plates  and  sulphuric  acid  is  far  from  being  understood  by  chemists. 
Almost  any  reversible  type  of  primary  cell  may  be  termed  a  storage 
battery,  because  of  its  reversibility.  The  original  condition  of  the 
electrodes  and  electrolyte  may  be  re-established  after  a  general  altera- 
tion has  been  wrought.  To  give  a  simple  example,  let  us  immerse 
in  a  beaker  containing  dilute  sulphuric  acid,  a  stick  of  chemically 
pure  zinc  and  a  strip  of  platinum.  We  have  learned  from  our 
previous  study  of  the  primary  cell  that  no  chemical  action  will  take 
place  unless  suitable  wires  are  joined  to  these  two  metals  and  brought 
into  contact  as  in  an  external  circuit.  We  will  then  have,  as  we 
know,  zinc  ions  being  forced  into  solution  and  hydrogen  ions  discharg- 
ing upon  the  platinum  electrode.  An  electrical  current  flows  through 
the  wire  connector  and  after  a  time  the  electromotive  force  will  be 
found  to  fall.  An  analysis  of  the  dilute  sulphuric  acid  will  reveal 
le  presence  of  zinc  sulphate,  and  we  have  seen  that  a  certain  quan- 

237 


238  EXPERIMENTAL  ELECTROCHEMISTRY. 

tity  of  hydrogen  has  escaped  as  gas.  There  will  be  minute  bubbles 
of  hydrogen  clinging  to  the  platinum,  however,  and  it  is  due  to  this 
fact  that  we  have  the  phenomenon  of  polarization.  By  adding 
potassium  dichromate  to  the  dilute  acid  solution  we  can  effectually 
prevent  the  formation  of  the  hydrogen  bubbles  and  maintain  a 
more  constant  electromotive  force.  We  can  also  bring  about  this 
depolarization  by  substituting  a  rod  of  copper  oxide,  for  example, 
for  the  platinum,  which  will  be  reduced  to  metallic  copper  by  the 
hydrogen  liberated  upon  its  surface.  The  cell  will  then  furnish  a 
certain  amount  of  current  and  do  a  definite  amount  of  work. 
There  will  be  found  no  sulphuric  acid  left,  but  a  concentrated  solu- 
tion of  zinc  sulphate  instead.  The  zinc  electrode  has  been  partly 
consumed.  The  zinc,  of  course,  has  displaced  in  the  acid  the 
hydrogen,  which  is  set  free.  Upon  sending  an  electrical  current 
through  the  cell  in  the  reversed  direction,  however,  the  cell 
is,  incorrectly  speaking,  recharged.  The  "charge"  in  the  present 
case  consists  in  the  deposition  of  the  zinc  through  the  zinc  sulphate 
upon  the  zinc  electrode  and  the  reformation  of  sulphuric  acid. 
Theoretically  speaking,  therefore,  the  only  thing  lost  during  the 
discharge  and  charge  of  this  particular  cell  is  hydrogen  and  oxygen 
gas  in  the  proportion  in  which  they  unite  to  form  water.  Such  a 
storage  cell  is  not  of  a  practical  nature,  however,  and  has  simply 
been  introduced  to  show  the  general  principle  upon  which  reversible 
cells  depend.  Let  us,  in  our  study  of  the  lead -lead-sulphuric  acid 
accumulator,  or  storage  battery,  experiment  a  little,  and  for  this 
purpose  we  may  best  begin  by  constructing  a  simple  cell,  study  its 
practical  behavior  by  charging  and  discharging  it,  and  examine 
the  plates  and  electrolyte,  by  experimental  methods,  before  we 
look  into  the  theory.  Fortunately,  there  is  no  more  easily  con- 
structed type  of  cell  than  a  simple  storage  battery.  For  our  experi- 
mental purpose  let  us  construct  a  cell,  as  illustrated  in  Fig.  113. 
We  may  use  a  rectangular  glass  cell  or  large  beaker.  A  rectangular 
glass  cell  is  preferable,  however,  and  one  about  6  inches  high  and 
about  6  inches  long  by  2  J  inches  wide  will  answer  our  requirements. 
A  rectangular  glass  jar  is  to  be  preferred,  for  the  reason  that  the  lead 
plates  required  may  be  cut  in  a  convenient  shape  to  hang  over 
the  mouth  of  the  jar.  These  lead  plates  should  be  cut  from  sheet 
lead,  not  over  J  of  an  inch  in  thickness,  and  may  be  provided  with 


THE  SECONDARY  CELL. 


239 


lugs  and  shoulders,  as  shown  by  the  diagram  of  the  plate  in  the  center 
of  the  illustration.  To  assemble  and  charge  such  a  cell  we  will 
put  into  the  jar  an  electrolyte,  consisting  of  one  part  of  concentrated 
sulphuric  acid  sp.  gr.  1.84  to  ten  parts  of  distilled  water.  The 
lead  electrodes  are  immersed  therein  after  having  been  thoroughly 
cleaned  by  dipping  them  into  dilute  nitric  acid,  if  the  lead  was  not 
perfectly  free  from  impurities  beforehand.  A  small  cell  of  this 
character  may  be  easily  charged  in  a  very  few  minutes  by  connecting 
it  to  the  motor-generator  and  supplying  about  8  amperes  to  it  under 
a  potential  difference  of  not  less  than  4  volts.  The  cell  may  also 
be  charged  by  including  it  in  the  no-volt  electric  lighting  circuit 


FIG.  113.  — Easily  Constructed  Experimental  Secondary  Cell. 


with  a  couple  of  lamps  in  multiple  arc.  The  primary  effect  of 
the  electric  current  is  to  decompose  the  water  between  the  lead 
electrodes.  The  liberated  hydrogen  escapes  from  the  cathode, 
therefore,  and  the  electrolytic  oxygen  from  the  anode.  The  anode 
plate,  if  perfectly  bright,  may  be  seen  to  darken  under  the  oxidizing 
action  of  the  electrolytic  oxygen,  whereas  the  cathode  assumes  a 
characteristic  lead -gray  color.  For  the  first  few  moments,  until  the 
two  electrodes  are  reduced  and  oxidized  respectively,  there  may  be 
no  oxygen  and  hydrogen  liberated.  The  oxygen  is  oxidizing 
the  metallic  lead  on  the  one  hand,  and  the  hydrogen  is 
reducing  any  oxides  which  may  be  upon  the  opposite  electrode, 
on  the  other  hand.  After  a  while,  however,  bubbles  of  gas  will 


240 


EXPERIMENTAL   ELECTROCHEMISTRY. 


appear  at  the  cathode  and  soon  afterwards  at  the  anode,  when  any 
further  current  furnished  will  not  go  to  charging  the  cell,  but  be 
expended  in  electrolizing  the  acidulated  water  present  without 
any  further  useful  end. 

The  central  diagram  in  Fig.  113  illustrating  the  form  of  lead 
electrode  also  indicates  in  the  shaded  portion  A,  the  manner  in 
which  the  lead  oxide  leaves  the  surface  of  the  oxidized  plate  on 
discharge.  By  referring  to  Fig.  114,  this  plate  is  shown  in  three 


FIG.   114. — Diagram  Showing  the  Appearance  of  the  Positive  Plate  in  Three 
Stages  of  Discharge. 

stages  of  discharge  When  the  cell  is  completely  charged  the  entire 
surface  of  the  annode  or  positive  electrode  is  darkened  with  the 
oxide  film.  Upon  discharge,  however,  the  oxide  film  begins  to 
leave  or  retreat  from  the  bottom  and  also  the  sides  of  the  plate, 
the  diminishing  area  being  depicted  by  the  shaded  areas  B,  Cy 
and  D  in  the  figure.  It  is  of  interest  to  note  that  so  long  as  we 
have  a  small  area  of  this  oxide  film,  the  E.M.F  of  the  cell  is  prac- 
tically constant.  This  is  analogous  to  the  E.M.F.  of  a  primary 
cell  which,  as  we  saw,  is  a  fixed  value  whether  the  electrodes  are 
immersed  to  a  large  or  small  extent.  The  E.M.F.,  therefore,  is  again 
due  to  the  phenomenon  of  solution  tension.  If  we  fully  charge 
a  lead-lead-sulphuric-acid  accumulator  we  will  find  that  for  a  short 
period  of  time  the  cell  is  capable  of  giving  us  an  electromotive  force 
of  over  2  volts.  This  E.M.F.  has  but  a  very  short  duration,  and 
is  believed  to  be  due  to-  the  occlusion  of  hydrogen  by  the  cathode 
plate,  which,  after  repeated  charging  and  discharging,  assumes 
a  more  or  less  porous  and  spongy  character.  We  will  therefore  fre- 
quently obtain  from  storage  cells  having  porous  or  spongy  cathode 


THE   SECONDARY   CELL. 


241 


plates,  an  electromotive  force  as  high  as  2.4  volts  for  short 
periods  of  time.  After  we  have  charged  and  discharged  the  experi- 
mental cell,  with  which  we  are  dealing,  we  will  be  able  to  notice 
this  interesting  phenomenon.  If  now  we  allow  the  cell  to  do  work 
by  discharging  it  through  a  suitable  external  resistance,  interrupting 
the  current  momentarily  at  regular  intervals  and  measuring  its 
E.M.F.,  or  electrical  pressure,  we  will  find  it  to  be  a  trifle  under  2 
volts  and  -constant  up  to  a  certain  point,  when  its  value  falls  abruptly. 
In  other  words,  a  storage  battery  will  yield  a  good  current  at  a  con- 
stant voltage  for  a  certain  length  of  time,  when  the  bottom  will,  so 
to  speak,  fall  out  all  at  once.  By  referring  to  the  diagram  in  Fig.  115, 


LI 

Z.3 

L.I 
I.I 

Jt.  0 


/     2      3 


f    /•///* 


// 


FIG.  115.  —  Diagram  Illustrating  the  Character  of  Discharge  of  a  Secondary  Cell. 

the  discharge  of  a  typical  storage  battery  is  plotted  in  the  form  of  a 
curve  for  twelve  hours.  According  to  this  diagram  the  cell  gave  a 
current  under  a  difference  of  potential  of  a  trifle  less  than  2  volts, 
when  an  abrupt  falling  off  of  the  electromotive  force  was  noted. 
For  twelve  hours,  therefore,  we  may  refer  to  the  cell  as  having  a 
horizontal  line  of  discharge.  This  is  an  idealized  curve,  for  in 
practice  this  discharge  -line  is  never  perfectly  horizontal,  although 
very  nearly  so.  We  should  plot  such  a  curve  with  our  storage  cell 
by  reading  a  delicate  volt  -meter  across  the-  electrodes  at,  let  us  say, 
minute  intervals  without  interrupting  the  flow  of  the  current  in 
the  external  circuit.  We  should  now  experimentally  determine  the 
changes  which  take  place  in  the  electrolyte,  that  is  to  say  the  density 


242 


EXPERIMENTAL  ELECTROCHEMISTRY. 


changes  that  are  wrought  in  the  sulphuric  acid  solution  upon  charge 
and  discharge. 

During  the  discharge  of  a  cell  of  battery  the  density  or  specific 
gravity  of  the  electrolyte  falls,  and  increases  again  on  charging.  By 
knowing  the  density,  therefore,  at  the  point  of  full  charge,  and  at 
full  exhaustion,  we  may  learn  something  of  the  state  of  the  cell 
between  those  points  by  specific  gravity  determinations.  For  our 
experimental  cell  a  sensitive  type  of  hydrometer  may  be  employed, 
as  depicted  in  Fig.  116.  This  peculiar  construction  is  the  design 


FIG.   116. — Author's  Sensitive  "Reflecting  Hydrometer"  for  Observing  Minute 
Density  Changes. 

of  the  author  as  applied  to  storage -battery  study  in  1895.  It 
consists  of  an  ordinary  glass  hydrometer  equipped  with  a  metal  cap 
with  a  V-shape  bearing  to  support  a  small  knife  edge  on  the  end 
of  an  aluminum  beam.  The  other  end  of  this  aluminum  beam 
is  equipped  with  a  similar  knife  edge,  which  rests  in  a  like  V-shape 
bearing,  mounted  upon  a  standard  which  is  carried  by  a  float.  This 
float  is  provided  with  a  central  aperture,  not  unlike  that  in  a  cake 
dish  through  which  the  stem  of  the  hydrometer  passes.  A  tiny 
mirror  is  mounted  on  one  end  of  this  aluminum  bar,  to  receive 
a  beam  of  light  which  it  reflects  upon  a  scale  analogous  to  that  on 
the  reflecting  galvanometer,  only  in  the  present  case  the  scale  is  ver- 
tical in  place  of  being  horizontal.  It  will  now  be  appreciated,  from 
a  glance  at  the  diagram,  that  the  minutest  changes  in  specific  gravity 
may  be  noted  by  the  movement  of  the  spot  of  reflected  light  upon 
the  graduated  scale.  Another  form  of  specific  gravity  indicator 
which  will  prove  useful  in  our  experimental  study  of  the  cell  is 


THE   SECONDARY   CELL. 


243 


illustrated  in  Fig.  117,  which  is  the  design  of  Mr.  J.  S.  Sellon,  and 
although  not  so  delicate  as  the  one  just  described,  has  a  useful  and 
practical  application  for  experimental  work.  We  can  now  charge 
and  discharge  our  cell,  measuring  the  energy  supplied  and  the 
energy  delivered,  examine  the  electrodes  and  their  behavior,  and  the 


FIG.  117. — Sellon's  Design  of  Hydrometer  as  Applied  to  Secondary  Cells. 

physical  changes  which  take  place,  such  as  the  density  alterations 
in  the  electrolyte.  What  now  can  be  said  regarding  the  theory  of  this 
type  of  battery  ?  It  would  appear  at  first  sight  to  be  an  easy  matter 
when  we  have  such  simple  elements  entering  into  the  construction 
as  pure  lead  plates  and  dilute  sulphuric  acid.  Unfortunately,  if  we 
attempt  to  follow  theoretically  the  transformations  which  takes  place 
in  a  complete  cycle,  that  is  to  say  the  charging  and  discharging  of  a 
secondary  cell,  we  will  find  that  we  become  lost  a  number  of  times  in 
the  determination. 

Regarding  the  chemistry  of  the  storage  battery  in  view  of  the 
exceedingly  difficult  chemical  problems  involved,  we  will  do  well 
to  quote  from  Professor  Ayrton's  paper  on  the  "Chemistry  of 
Secondary  Batteries.'' 


244 


EXPERIMENTAL   ELECTROCHEMISTRY. 


"The  physical  qualities  of  the  cells  are  capable  of  very  accurate 
estimation  and  investigation.  But  when  you  come  to  attempt  to 
ascertain  the  chemical  changes  that  occur  in  the  charging  and  dis- 
charging of  a  storage  cell  you  encounter  formidable  difficulties. 
The  outsider  has  no  idea  of  these  difficulties.  Nothing  seems  more 
simple  than  to  determine  the  chemical  changes  that  take  place  in 
either  the  positive  or  the  negative  plate  of  a  storage  battery.  It 
is  not  so  in  reality.  The  substances  used  as  actve  materials  are 
in  the  first  place  mixtures,  and  the  materials  obtained  at  the  end 
of  the  reactions  are  also  mixtures,  and  these  mixtures  are  insoluble 
in  any  reagent  which  does  not  decompose  them.  They  cannot  be 
volatilized;  they  cannot  be  subjected  to  any  process. of  solution  and 
crystallization  in  order  to  separate  and  purify  their  elements." 

There  are,  however,  several  theories  advanced  to  account  for 
the  charging  and  discharging  of  a  storage  battery,  and  we  would 
do  well  to  consider  some  important  ones  here.  Let  us  first  take 
up  the  theory  of  Plante. 

The  first  diagram  illustrates  the  effect  of  the  electric  current  in 
the  formation  of  sulphate  of  lead  by  the  substitution  of  lead  for  the 
hydrogen  in  the  sulphuric  acid. 

T 

H2S04      H2S04      H2S04      Pb 


The  second  diagram  shows  the  production  of  persulphuric  acid 
by  the  elimination  of  a  further  molecule  of  hydrogen. 

T 

H2S04      H2S03      O 


o 
% 

The  third  diagram  shows  how  the  formation  of  peroxide  of  lead 
may  take  place  by  the  reaction  between  persulphuric  acid  and  sul- 
phate of  lead  in  the  presence  of  water. 


H2S2O8  ) 
2H20      f 


THE   SECONDARY   CELL. 


245 


The  fourth  diagram  shows  the  production  of  a  second  molecule 
of  persulphuric  acid  by  the  current  proceeding  from  the  peroxide- 
coated  anode,  and  also  the  decomposition  of  the  persulphuric  acid, 
in  the  presence  of  water,  which  results  in  the  formation  of  peroxide 
of  hydrogen  and  the  reformation  of  sulphuric  acid. 


TJ 
H2S04      H2S03      0  g 

H2S208  } 
2H2O     C 

]H202 
1  2H2SO4 

Another  theory  of  the  storage  battery  is  as  follows  :  During  the 
discharge  of  a  cell  both  electrodes  are  converted  into  lead  sulphate 
with  the  abstraction  of  SO4  from  the  electrolyte,  which  diminishes 
its  specific  gravity.  The  change  on  the  anode  or  positive  electrode  is 
believed  to  take  place  in  two  separate  stages:  First,  the  reduc- 
tion of  the  peroxide  of  lead  to  the  monoxide,  and  then  the  conversion 
of  the  monoxide  of  lead  into  the  sulphate  of  lead.  When  the 
cell  is  charged  we  have  the  reverse,  the  sulphate  of  lead  being 
converted  into  the  peroxide  on  the  positive  plate  and  metallic  lead 
on  the  negative  plate  or  electrode.  According  to  Tread  well,  the 
generally  accepted  theory  at  present  is  that  of  the  direct  formation 
of  lead  sulphate  at  both  electrodes,  "each  molecule  of  the  peroxide 
is  supposed  to  loose  an  atom  of  oxygen,  and  each  atom  of  spongy 
lead  to  gain  an  atom  of  oxygen.  Two  molecules  of  hydrogen  sul- 
phate are  thus  abstracted  from  the  electrolyte  to  react  with  the 
peroxide  or  spongy  lead,  and  their  places  are  taken  by  2  molecules 
of  water. 


and  that  for  the  negative  plate  is 

Pb  +  O  +  H2SO4  =  PbSO4  +  H2O  ; 
or,  including  both  reactions  in  one  equation, 

PbO2  +  2H2SO4  +  Pb  =  PbSO4  +  2H2O  +  PbSO4. 

"  Thus  the  final  result  of  the  complete  discharge  of  a  cell  is  to 
form  lead  sulphate  and  water  by  removing  sulphuric  acid  from  the 
electrolyte  and  depositing  sulphate  of  lead  upon  each  plate. 


246  EXPERIMENTAL   ELECTROCHEMISTRY. 

"  The  above  is,  fortunately,  a  self -limiting  process,  since  the  sul- 
phate is  a  poor  conductor.  All  the  peroxide  is  therefore  not  acted 
upon,  and  at  the  end  of  the  discharge  we  have  peroxide  of  lead 
crystals  covered  with  a  coating  of  sulphate." 

So  much  for  the  study  of  conditions.  The  cell  illustrated  in  Fig. 
113  is  of  the  simplest  possible  type,  and,  because  of  the  limited 
electrode  area  of  smooth  metallic  lead,  has  but  a  very  low  current 
capacity.  When  fully  charged  it  will  give  a  current  for  but  a  few 
moments,  and  for  this  reason  is  only  adapted  for  the  briefer  kind  of 
research  and  study.  This  battery  can  be  increased  in  capacity  by 
roughening  the  lead  plates  through  the  agency  of  a  knurl  or  other 
suitable  tool. 

The  battery  can  also  be  wonderfully  increased  in  efficiency  by 
not  only  roughening  the  anode  or  positive  plate,  but  by  preparing 
it  by  filling  it  in  with  active  material.  The  practical  cells  of  battery 
on  the  market  to-day  consist  of  such  specially  prepared  plates,  which 
are  termed  grids.  It  would  be  almost  impossible  to  describe  or 
illustrate  the  various  designs  or  types  of  grids  intended  to  meet  the 
rather  trying  conditions  of  practice.  Perforations  of  every  conceivable 
shape  and  size,  grooves,  mat-work,  applications  of  disks,  buttons, 
chambers,  etc.,  etc.,  have  been  devised  in  order  to  hold  the  active 
material,  prepared  in  numerous  ways,  to  form  the  positive  plate.  It 
would  require  a  special  treatise  on  the  storage  battery  to  begin  to 
illustrate  and  to  do  justice  to  the  numerous  ingenious  designs  of 
storage -battery  electrodes.  Apart  from  designing  a  positive  plate 
for  maximum  efficiency  for  receiving  and  holding  the  active  peroxide 
of  lead,  we  must  design  an  electrode  which  will  not  "  buckle"  under 
working  conditions.  Buckling,  in  storage-battery  parlance,  is  the 
warping,  twisting,  and  bending  of  an  electrode  due  to  the  inequalities 
in  expansion  between  the  active  material  and  the  supporting  grid 
or  lead  work  during  charge  or  discharge.  With  certain  types  of 
electrodes  this  evil  is  manifested  if  a  battery  is  charged  too  quickly 
or  allowed  to  give  up  its  available  current  jn  too  short  a  period  of 
time.  Twisting  or  buckling  of  the  electrode  of  a  storage  cell,  not 
only  ruins  the  plates,  but  interrupts  the  duty  of  the  cell  in  a  battery 
because  of  the  short-circuiting  which  is  brought  about.  A  modern 
storage  battery  of  large  capacity  is  a  rather  costly  thing,  and  in 
the  hands  of  incompetent  attendants  may  be  easily  damaged. 


THE   SECONDARY   CELL.  247 

Among  the  precautions  in  the  care  of  the  storage  battery  may  be 
mentioned  the  desirability  of  having  the  electrolyte  perfectly  homo- 
geneous, that  is  to  say,  free  from  strata  of  different  acid  concentra- 
tions, which  will  bring  about  uneven  action  upon  the  electrode. 
Great  care  should  be  taken  to  prevent  foreign  bodies  from  falling 
in  between  the  plates,  and  to  supply  pure  water  to  make  up  for  loss 
due  through  electrolysis  and  evaporation.  The  battery  should 
be  charged  at  either  constant  voltage  or  constant  current,  the 
current  being  supplied  to  the  battery  under  a  potential  difference 
only  a  little  higher  than  that  of  the  battery  itself.  For  example,  if 
we  wish  to  charge  ten  cells  of  storage  battery  in  series,  a  current 
under  a  pressure  of  about  30  volts,  will  be  good  practice.  In  the 
charging  oi  a  single  cell,  therefore,  we  should  not  seek  a  high-pres- 
sure current,  but  would  prefer  one  with  a  voltage  of  about  2\  to  3 
volts.  In  charging  the  battery,  we  must  know  the  current  density 
conditions  which  the  battery  will  stand,  that  is  to  say,  we  should  not 
supply  too  many  amperes  per  square  foot  of  electrode  area.  The 
same  question  is  involved  when  the  battery  is  allowed  to  do  work, 
and  may  be  injured  as  a  dynamo  may  be  injured  if  allowed  to  dis- 
charge through  an  external  circuit  of  too  low  a  resistance.  In  the 
case  of  the  battery  we  are  liable  to  have  buckling  due  to  the  heavy 
current  passing,  and  in  the  case  of  the  dynamo  we  are  liable  to  burn 
out  the  armature.  Too  large  a  charging  current,  apart  from  the 
liability  of  injuring  the  battery,  is  very  uneconomical,  for  a  good 
deal  of  the  electrical  energy  is  transformed  into  heat.  We  should, 
therefore,  keep  the  charging  current  comparatively  low  if  we  seek 
economy,  unless  the  time  of  charging  is  to  be  counted  as  one  of 
the  elements  in  cost.  Too  low  a  charging  current,  on  the  other 
hand,  is  also  injurious  to  the  cell,  for  it  is  found  to  produce  the  white 
sulphate  of  lead  upon  the  positive  plate,  instead  of  the  active  per- 
oxide, which  we  seek.  Gladstone  and  Tribe,  in  their  work  entitled, 
"  Chemistry  of  Secondary  Batteries,"  bring  out  this  point  as  follows: 
"If  we  take  two  plates  of  lead  in  dilute  sulphuric  acid  and 
pass  a  current  from  only  one  Grove  cell,  a  film  of  white  sulphate, 
instead  of  peroxide,  makes  its  appearance  on  the  positive  plate, 
and  the  action  practically  ceases  very  soon.  If,  however,  the  current 
is  increased  in  strength,  the  sulphate  disappears,  and  peroxide 
is  found  in  its  place." 


*48          EXPERIMENTAL  ELECTROCHEMISTRY. 

With  a  good  battery  a  safe  rule  to  follow  is  to  furnish  current 
to  the  extent  of  about  8  amperes  per  square  foot  of  electrode  area. 
After  a  battery  has  been  fully  charged,  oxygen  and  hydrogen 
gases  are,  of  course,  given  off  at  both  electrodes,  and  the  energy 
which  we  are  furnishing  the  cell  merely  goes  to  the  decomposition 
of  water  with  the  setting  free  of  the  component  gases.  This  con- 
dition is  termed  "boiling,"  which  does  not,  as  we  have  seen,  refer 
to  any  phenomenon  due  to  heat,  but  merely  to  the  setting  free  of 
large  volumes  of  gas.  In  charging  a  battery  it  should  never  be 
allowed  to  fully  discharge,  about  30  per  cent  of  the  available  energy 
being  left  in  every  case.  The  voltage  of  a  storage  cell  under  load 
should  not  be  allowed  to  fall  below  1.8.  When  a  cell  is  left  to  stand 
without  doing  work,  it  should  be  fully  charged. 

There  are  several  methods  for  calculating  the  capacity  of  a 
storage  cell  in  ampere-hours,  and  as  they  are  purely  electrochemical 
in  character  should  be  touched  upon  before  we  close  the  present 
chapter.  The  number  of  coulombs  maintained  by  the  consump- 
tion of  a  chemically  active  substance  varies  with  the  change  of  valence 
and  inversely  with  the  molecular  weights  of  the  transforming  sub- 
stance. According  to  Treadwell,  the  combustion  or  liberation  of 
one  pound  of  hydrogen  corresponds  to  12,160  ampere-hours. 

The  theoretical  current  capacity,  therefore,  in  ampere-hours 
may  be  figured  from  the  following  rule: 

"  F=the  change  of  valence  of  the  ions; 
W  =  the  sum  of  the  molecular  weights  affected,  and 
1 2, 1 60=  the  capacity  per  pound  of  hydrogen. 

i2i6oXF  „ 
Then  capacity  per  pound  = ^ . 

Regarding  lead  sulphate,  which  is  the  ultimate  product  at  both 
electrodes,  we  obtain  as  the  value  of  the  active  material  by  the  use 
of  the  above  formula  40.24  ampere-hours,  or  80.48  watt-hours,  per 
pound  of  lead  sulphate,  with  the  lead-lead-sulphuric-acid  battery. 

For  the  calculation  of  electromotive  force  of  storage  cells  we 
have  the  following  from  "Chemical  Theory  of  Accumulators,"  by 
E.  J.  Wade. 


THE   SECONDARY   CELL.  249 

TF  =  the  work  in  joules. 

Q=the   coulombs   of  electricity  that   are   passed   throiigh   the 

electrolyte. 
5"  =  the  number  of  calories  liberated  by  the  recombination  of  a 

unit  weight  of  one  of  the  decomposed  ions. 
e  =  its  electrochemical  equivalent. 
£  =  its  chemical  equivalent. 
h  =  the  electrochemical  equivalent  of  hydrogen 

=  .00001038. 

J  =  Joule's  coefficient  =  4.  2 
£  =  the  E.M.F.  required. 

W  =  QE, 
W-QJeH; 

therefore  E  =  deH 

and  e  =  he; 

therefore  E  =  JhcH  =  4.2X.ooooio^S>cH 


heat  of  formation 
Now,  cH  =  - 


therefore  E  = 


valency 
.  0000436  X  heat  of  formation 
valency 


Since  nearly  all  the  battery  equations  are  expressed  in  terms  of  the 
transfer  of  two  atoms  of  hydrogen,  or  their  equivalent  (that  is, 
they  are  bivalent),  and  since 

.0000436X46000  =  1  volt 
~1T~  ' 

heat  of  formation  in  calories 


. 
we  have  E 


7 
46000 


CHAPTER  XVIII. 
ELECTRICITY  'FROM   CARBON. 

THERE  are  few  problems  known  to  man  that  promise  such  a 
fruitful  reward  to  the  advancement  of  scientific  triumph  as  the  one 
pertaining  to  the  direct  conversion  of  the  energy  of  carbon  into  elec- 
tricity. The  benefits  to  be  obtained  from  the  solution  of  this  greatest 
of  electrochemical  possibilities  are  practically  without  words  to 
express.  We  have  on  earth  but  few  prime  movers  when  we  carefully 
look  into-  and  consider  the  situation.  By  prime  movers  we  mean  a 
direct  source  of  energy.  Electricity  in  its  dynamic  form,  and  with 
its  applications  for  purposes  of  doing  work,  is  but  a  secondary  power. 
When  -we  consider  the  question  from  the  basic  point  of  view,  we  find 
as  tabulated  by  Joseph  Henry  in  his  Scientific  Writings,  published 
by  the  Smithsonian  Institution,  the  following  interesting  and  historic 
list: 

i*  Water-power. 
(2.  Wind-power. 

3.  Tide-power. 

4.  The  power  of  combustion. 

5.  The  power  of  vital  action. 

Continuing,  he  writes:  "To  this  list  may  hereafter  be  added  the 
power  of  the  volcano  and  the  internal  heat  of  the  earth;  and,  besides 
these,  science  at  the  present  time  gives  no  indications  of  any  other. 
These  are  denominated  primary  powers,  though  in  reality,  when 
critically  studied,  they  may  all,  except  the  two  last  mentioned,  be 
referred  to  actions  from  without  the  earth,  and  principally  to  emana- 
tions from  the  sun. 

"  Gravitation,  electricity,  galvanism,  magnetism,  and  chemical 
affinity  can  never  be  employed  as  original  sources  of  power.  At 

the  surface  of  the  earth  they  are  forces  of  quiescence,  the  normal 

250 


ELECTRICITY   FROM   CARBON.  251 

condition  of  which  must  be  disturbed  before  they  can  manifest 
power,  and  then  the  work  which  they  are  capable  of  performing  is 
only  the  equivalent  of  the  power  which  was  communicated  to  them. 

"  There  is  no  more  prevalent  and  mischievous  error  than  the  idea 
that  there  is  in  what  are  called  the  'imponderables'  a  principle  of 
spontaneous  activity.  Heat  is  the  product  of  chemical  action,  and 
electricity  only  manifests  power  when  its  equilibrium  is  disturbed 
by  an  extraneous  force,  and  then  the  effect  is  only  proportional  to 
the  disturbing  cause.  It  was  for  this  reason  that  the  existence  of 
electricity  remained  so  long  unknown  to  man.  Though  electricity  is 
not  in  itself  a  source  of  power,  yet  from  its  extreme  mobility  and  high 
elasticity  it  affords  the  means  of  transmitting  power  with  scarcely  any 
loss  and  almost  inconceivable  velocity  to  the  greatest  distance.  A 
wave  of  disturbance  starting  from  the  impulse  given  at  the  battery 
will  traverse  the  circumference  of  the  earth  in  less  time  than  I  have 
been  occupied  in  stating  the  fact. 

"  Besides  electricity  and  the  principle  before  mentioned,  there  are 
other  agents  employed  between  the  primary  power  and  the  work, 
namely,  the  elastic  force  of  steam,  of  air,  and  of  springs ;  also  vari- 
ous instruments  called  machines.  But  these  must  not  be  confounded, 
as  they  frequently  are,  with  the  sources  of  power.  It  is  not  the 
engine  Which  is  the  source  of  motion  of  the  cars,  nor  yet  the  steam, 
but  the  repulsive  energy  imparted  to  the  expanding  water  from  the 
burning  fuel." 

Through  the  agency  of  the  steam-engine  we  obtain  mechanical 
energy  which  drives  the  dynamo  for  the  production  of  electricity. 
In  this  system,  with  its  several  transformations,  the  electricity 
delivered  at  the  terminals  of  the  machine  is  traced  back  through 
the  rotating  armature  with  its  necessary  losses,  through  the  belt  or 
shaft  to  the  engine  with  its  friction  and  radiation,  to  the  boiler  with 
its  many  sources  of  waste,  and  thence  to  the  grate-bars  where  heat 
results  from  the  oxidation  of  the  carbon  supported  there.  It  is 
estimated  that  only  5  or  6  per  cent  of  the  available  energy  of  the 
carbon  is  transformed  into  useful  work.  If  now  it  were  possible 
within  a  suitable  cell  to  obtain  as  a  result  of  the  oxidation  of  carbon 
the  electric  current  direct  without  the  production  of  heat,  what  a 
majestic  discovery  would  be  made! 

There  is  no  principle  of  science  standing  in  our  way,  and  yet 


252  EXPERIMENTAL   ELECTROCHEMISTRY. 

the  brightest  minds  in  physical  and  chemical  science  have  been 
unable  to  solve  the  problem.  Heat  energy  may  be  transformed  into 
electrical  energy,  mechanical  energy  into  heat  energy,  mechanical 
energy  into  electrical,  etc.,  etc.,  etc.,  without  gain  or  loss,  as  we 
learned  from  the  great  doctrine  of  the  conservation  and  correlation 
of  energy.  Instead  of  getting  heat  energy  from  carbon  we  can, 
as  far  as  existing  conditions  of  science  indicate,  obtain  electricity 
direct.  From  the  grate-bars,  boiler,  engine,  and  dynamo  with  their 
combined  miserable  showing  of  5  or  6  per  cent  energy  yield,  we  may 
turn  for  an  instant  to  the  primary  cell.  Here  we  obtain  electricity 
direct  from  what  we  may  term  the  combustion  of  zinc,  by  immers- 
ing pure  zinc  and  platinum  electrodes  in  dilute  sulphuric  acid, 
with  a  current  yield  as  high  as  90  per  cent  of  that  theoretically 
possible.  Zinc  is  too  costly  a  fuel,  however,  except  in  special  cases 
and  upon  a  very  small  scale,  and  it  has  been  the  goal  of  chemists 
and  physicists  to  discover  a  method  for  obtaining  electricity  as  a 
direct  result  of  the  combustion  of  carbon  or  coal.  In  taking  up  the 
consideration  of  this  problem  in  the  present  chapter,  the  writer 
wishes  to  warn  the  student  not  to  confuse  thermoelectric  deport- 
ment with  the  problem  we  really  have  in  hand.  Many  investi- 
gators have  obtained  electricity  by  using  carbon  rods  in  connection 
with  electrodes  of  different  composition  immersed  in  a  fused  elec- 
trolyte, but  the  source  of  electricity  has  been  ultimately  traced,  not 
to  the  primary  combustion  of  carbon,  but  to  thermoelectric  action. 
Because  of  the  still  existing  likelihood  of  research  students  going 
astray  in  working  on  this  great  problem,  it  may  be  wise  to  introduce 
the  subject  of  thermoelectric  action  first,  and  acquaint  him  with  the 
conditions  for  its  existence  before  the  problem  of  the  direct  con- 
version of  the  energy  of  carbon  into  electricity  is  dealt  with.  It 
was  in  1821  that  Prof.  Seeback  of  Berlin,  noticed  that  by  heating 
a  junction  of  two  metals  in  a  circuit  an  electric  current  was  produced. 
The  thermoelectric  current  has  been  shown  by  heating  the  junction 
between  two  dissimilar  metals  of  a  circuit  which  surrounds  a  mag- 
netic needle  whereby  its  direction  is  noted.  If  now  the  source  of 
heat  be  removed  from  this  junction,  and  it  be  cooled  by  a  little  ice 
or  some  absorbent  cotton  moistened  with  ether,  an  electrical  current 
will  be  indicated  by  the  magnetic  needle  but  of  opposite  direction 
of  flow.  A  thermoelectric  couple  for  experimental  purposes  may 


ELECTRICITY   FROM   CARBON. 


253 


be  easily  constructed  by  joining  together  two  different  metals  at 
their  lower  ends,  as  indicated  in  Fig.  118,  and  leading  wires  from 
the  upper  ends  of  a  galvanometer,  or  milli-volt-meter.  If  the  lower 
junction  is  now  heated  there  will  be  a  current  set  up,  as  indicated 
by  the  little  arrow,  from  the  positive  to  the  negative  metal.  The 
electromotive  force  of  this  current  may  be  increased  by  connecting 
together  a  number  of  bars,  as  shown  at  the  right  in  this  illustration, 
and  heating  all  the  lower  junctions  and  keeping  the  upper  ones 


1 

^L 

i 

§c 

1 

^ 

i 

FIG.  1 18. — Typical  Thermoelectric  Couplers. 


cool.  It  is  upon  this  plan  that  the  most  delicate  thermometers, 
or  heat  detectors  have  been  devised.  Numerous  designs  of  thermo- 
electric batteries  have  also  been  produced,  some  few  of  them  having 
proven  quite  practical  in  operation,  giving  as  a  direct  exchange 
for  heat  energy  energy  in  the  form  of  electricity.  Fig.  119  shows 
an  old  form  of  thermoelectric  battery  of  more  scientific  interest  than 
practical  value.  It  has  been  found  that  a  couple  made  of  bismuth 
and  antimony  heated  at  the  point  of  union  corresponds  .very  closely 
in  electromotive  force  to  a  couple  consisting  of  zinc  and  copper 
immersed  in  sulphuric  acid.  Couples  have  been  made  of  many  of 
the  available  metals,  as  well  as  from  carbon,  and  electrical  currents 
obtained  under  different  potentials.  At  the  point  of  contact  between 
dissimilar  conductors  of  electricity,  whether  of  the  metals  or  of  carbon 
and  a  metal,  electricity  is  set  up  in  the  form  of  a  current  when  such 
contact  or  junction  is  heated.  It  is  for  us  to  realize  this  and  take 


254 


EXPERIMENTAL   ELECTROCHEMISTRY. 


it  into  account  in  any  work  we  may  do  with  direct  conversion  of 
carbon  into  electricity.  Of  all  the  attempts  to  reach  a  solution 
of  this  great  problem  by  men  with  every  type  of  equipment,  from 
the  haphazard-try-and-learn  character  to  the  research  worker  with 
every  theoretical  equipment,  only  failure  has  resulted.  One  of  the 
great  difficulties  in  the  way  of  solving  this  problem  is  in  the  fact 
that  carbon  does  not  dissolve  in  suitable  electrolytes  by  the  simple 
throwing  off  of  the  positive  ions  of  the  carbon. 


FlG.  119. — Historic  Thermoelectric  Battery. 

As  early  as  1855  Bacquerel  conducted  an  experiment  as  illustrated 
in  Fig.  120.  A  rod  of  carbon  was  immersed  in  a  bath  of  fused 
nitre  contained  in  an  iron  or  platinum  spoon  in  order  to  bring  about 
the  oxidation  of  the  carbon  and  the  production  of  the  electric  current. 
A  galvanometer  included  in  the  circuit  gave  a  marked  indication. 
In  1877  Jablochkoff  repeated  the  experiment  on  a  large  scale  and 
under  certain  modified  conditions.  It  will  be  interesting  for  us  to 


ELECTRICITY   FROM    CARBON. 


255 


note  at  this  time  the  possible  theoretical  electromotive  force  obtain- 
able from  a  carbon  cell  when  the  carbon  is  oxidized  completely  to 
carbon  dioxide.  From  thermochemical  data,  it  has  been  estimated 
that  a  cell  in  which  carbon  is  completely  oxidized  to  carbon  dioxide, 
the  electromotive  force  obtainable  is  1.04  volts.  In  the  majority 
of  experiments  which  have  been  made  with  carbon  for  the  direct 
production  of  electricity,  the  most  incomplete  data  are  given.  Apart 
from  electromotive  force  indications  on  open  circuit  regarding  the 
deportment  of  cells,  no  current  data  are  to  be  found.  One  of  the 
most  recent  carbon  cells  is  that  of  W.  W.  Jacques,  in  which  a  carbon 
rod  is  immersed  in  fused  sodium  hydroxide,  contained  within  an 
iron  vessel,  heated  externally  by  a  furnace;  the  iron  pot  serving  as  a 


FIG.  120. — Bacquerel's  Experiment  on  the  Oxidation  of  Carbon  to  Electricity. 


positive  electrode,  while  the  carbon  is  the  negative.  Oxygen  is 
pumped  to  the  bottom  of  the  fused  caustic  soda  through  a  tube  ending 
in  a  ring  around  the  lower  end  of  the  carbon,  the  ring  being  provided 
with  perforations,  through  which  oxygen  under  pressure  escapes 
and  comes  in  contact  with  the  heated  carbon.  There  is  an  opening 
in  the  cover  of  this  cell  whereby  the  gaseous  products  of  oxidation 
escape.  Of  course,  air  may  be  pumped  into  the  electrolyte  in  the 
place  of  oxygen,  although,  for  obvious  reasons,  it  is  not  claimed  to 
be  so  efficient.  According  to  Jacques,  the  carbon  within  is  oxidized 
to  carbon  dioxide,  and  the  energy  produced  is  given  in  the  form  of 
an  electrical  current.  It  was  claimed  that  with  a  battery  of  100  cells 
a  current  of  about  15  amperes  was  obtained  for  18  hours  under 


256  EXPERIMENTAL   ELECTROCHEMISTRY. 

a  difference  of  potential  of  90  volts,  the  consumption  of  carbon 
being  about  8  pounds.  This  performance  corresponds  with  an 
efficiency  of  about  80  per  cent  based  on  that  theoretically  possible 
from  the  weight  of  carbon  oxidized.  This  calculation  does  not 
take  into  account  the  energy  expended  in  the  form  of  heat  to  keep 
the  electrolyte  fluid  or  the  energy  necessary  to  pump  the  air  or 
oxygen  through  the. fused  salt.  The  device  is  not  what  has  been 
claimed  for  it,  as  it  is  entirely  wrong  in  principle.  Research  upon 
this  cell  has  proven  that  the  electricity  does  not  come  at  all  from  the 
oxidation  of  the  carbon,  but  from  purely  thermochemical  action. 
The  substitution  of  other  electrodes  in  the  place  of  the  carbon -rod 
gives  us  practically  the  same  current.  If  the  carbon  was  oxidized 
to  carbon  dioxide-  gas  in  the  molten,  caustic  soda,  we  know,  as  general 
chemists,  that  it  would  be  rapidly  converted  into  sodium  carbonate, 
which  would  ruin  it  for  further  usefulness. 

Probably  the  majority  of  research  workers  on  this  problem  have 
immersed  a  carbon  rod  against  some  metal  in  a  strong  oxidizing 
agent,  fused  nitre  for  example,  in  the  hope  that  the  oxidation  of  the 
carbon  would  take  place  with  the  production  of  the  electric  current. 
In  other  words,  the  carbon  is  brought  in  direct  contact  with  oxidizing 
agents.  Such  a  course  is  manifestly  wrong  in  principle  when  we  look 
a  little  into  the  question  of  primary  cells.  If,  for  example,  we  wish 
to  obtain  electricity  by  the  consumption  of  zinc,  we  may  do  so  in 
several  ways.  We  would  undoubtedly  obtain  a  current  of  electricity 
if  we  put  a  rod  of  zinc  and  a  strip  of  platinum  in  strong  nitric  acid, 
but  the  practice  would  be  a  most  wasteful  one.  There  would  be 
some  electrical  current  produced,  but  most  of  the  energy  would 
appear  as  heat,  as  the  result  of  the  energetic  local  action  of  the 
nitric  acid  on  the  zinc.  To  quote  Ostwald  upon  the  subject  of 
electricity  from  carbon,  he  says:  "The  carbon  cell  of  the  future 
must  have  an  oxidizing  agent  in  the  place  where  the  carbon  is  not." 
To  make  this  statement  clear  he  refers  the  reader  to  the  experiment 
where  zinc  and  platinum  are  immersed  in  two  separate  vessels  con- 
taining a  solution  of  potassium  sulphate  and  separated  by  a  siphon- 
tube,  as  illustrated  in  Fig.  no-,  Chapter  XVI.  In  order  to  bring- 
about  the  economical  consumption  of  zinc  in  this  system  we  learn 
that  the  sulphuric  acid  must  not  be  added  to  the  beaker  containing 
the  zinc,  but  to  that  containing  the  platinum.  It  is  very  evident  that 


ELECTRICITY  FROM   CARBON.  257 

if  we  wish  to  obtain  electricity  direct  from  carbon,  as  we  do  from 
zinc  in  the  primary  cell,  some  electrolyte  must  be  discovered  in  which 
carbon  will  dissolve  with  the  formation  of  ions.  It  is  to-day  uncer- 
tain whether  or  not  carbon  ionizes  in  certain  solutions  under  the 
action  of  electricity,  opinion  being  divided  upon  this  question.  Al- 
though the  majority  of  electrochemists  do-  not  believe  in  the  ionization 
of  carbon  there  are  certain  experiments  which  tend  to  show  the 
contrary.  Papasogli  and  Bartoli  noticed  that  the  passage  of  an 
electric  current  between  carbon  electrodes  immersed  in  dilute  sul- 
phuric acid  was  accompanied  by  certain  marked  chemical  changes. 
The  carbon  serving  as  anode  is  believed  to  go  into  solution  for  the 
reason  that  carbon  monoxide  and  carbon  dioxide  gases  appear  as 
anode  products  together  with  the  oxygen.  Coehn,  in  working 
along  these  lines  was  able,  under  certain  conditions,  to  effect  the  con- 
sumption of  carbon  in  dilute  sulphuric  acid,  with  the  evolution  of 
carbon  monoxide  and  carbon  dioxide  gases,  in  the  proportion  of 
30  per  cent  carbon  monoxide  and  about  70  per  cent  carbon  dioxide, 
an  evolution  of  only  about  i  per  cent  of  free  oxygen  being  found. 
The  acid  assumed  a  reddish-brown  color  believed  to  be  due  to  the 
actual  dissolution  of  the  carbon.  If  the  electrolysis  is  allowed  to 
proceed  with  the  carbon  as  anode,  after  substituting  a  platinum 
cathode,  the  latter  becomes  covered  with  a  black  deposit.  This  has 
been  analyzed  and  found  to  consist  of  carbon  containing  occluded 
oxygen  and  hydrogen  gases  in  the  proportion  in  which  they  combine 
to  form  water.  Coehn  also  showed  that  an  electrode  of  carbon  and 
one  of  lead  peroxide  in  dilute  sulphuric  acid  produced  a  constant 
current  until  the  lead  peroxide  was  reduced  to  lead,  or  else  the  carbon 
consumed.  Of  all  the  attempts  to  dissolve  carbon  to  obtain  the  energy 
of  oxidation  as  electricity,  none  of  them,  however,  have  met  with 
any  real  success.  As  pointed  out,  there  are  numberless  cases  of 
experimental  research  with  the  most  varied  type  of  cell  for  the 
oxidation  of  carbon,  but  the  electrical  data  obtainable  are  exceedingly 
meagre.  In  most  of  the  reports  of  investigators,  only  a  statement  of 
electromotive  force  is  given  on  open  circuits,  whereas,  we  know  elec- 
trical data  pertaining  to  batteries  are  useless  unless  we  have  together 
with  the  electromotive  force  a  statement  regarding  the  number  of 
coulombs  the  cell  will  furnish.  As  many  of  the  cells  have  been 
upon  the  general  principle  of  Jacques,  an  illustration  of  one  of  them 


258 


EXPERIMENTAL   ELECTROCHEMISTRY. 


is  deemed  of  interest  here.  Fig.  121  represents  Edison's  design, 
where  we  have  a  furnace  for  heating  the  iron  melting-pot.  The 
cover  is  of  an  insulating  material  and  supports  the  carbon  electrode. 
The  electrolyte  is  chosen  from  the  oxidizing  agents,  like  nitre,  for 
example,  or  even  certain  oxides,  and,  according  to  Edison,  a  reduction 
of  the  compound  takes  place,  the  oxygen  combining  with  the  carbon 


FIG.   121. — Edison's  Cell  for  Obtaining  Electricity  from  Carbon. 


in  the  formation  of  carbon  monoxide,  which  may  be  piped  off  and 
used  for  fuel.  The  residue  resulting  from  the  reduction  of  the 
oxide  may  be  used  over  again  as  the  negative  agent  of  the  cell. 
From  what  we  have  seen  this  is  entirely  wrong  in  principle,  and 
the  electricity  obtained  is  primarily  of  thermoelectric  origin.  The 
problem  to-day  is  one  of  possible  solution,  but  no  practical  results 
have  as  yet  been  obtained.  To  enumerate  the  various  researches 
upon  this  important  problem  would  fill  a  book  in  itself. 


CHAPTER    XIX. 
USEFUL   PIECES    OF   APPARATUS. 

As  has  been  frequently  indicated  throughout  this  experimental 
work,  the  writer  believes  that  through  the  introduction  of  con- 
venient and  useful  types  of  apparatus  of  various  kinds,  the  student 
often  obtains  valuable  information  in  the  way  of  suggestions 
for  certain  lines  of  research.  It  is  believed  that  in  many  cases  the 
research  student  receives  much  benefit  from  a  diagram  of  apparatus, 
especially  if  he  possesses  ingenuity  and  has  initiative,  so  to  speak, 
for  investigation.  There  will  be  many  problems  in  electrochemistry 
confronting  the  experimenter,  some  of  which  require  special  types 
of  cells  in  order  that  certain  conditions  of  electrolysis  may  be 
established.  There  are,  in  addition,  pieces  of  apparatus  useful  in 
saving  time  because  of  their  most  convenient  design  and  application. 
For  rapidly  comparing  the  conductivities  of  various  electrolytes  in 
small  quantities  it  would  be  difficult  to  design  a  more  handy  and 
convenient  device  than  that  illustrated  in  Fig.  122.  This  cut  repre- 
sents a  special  form  of  pipette  equipped  with  a  ground  glass  stop-cock 
in  order  that  it  may  easily  be  held  filled  by  closing  the  stop-cock. 
Two  simple  platinum  disks  welded  to  stout  platinum  wires  are 
sealed  into  the  glass,  facing  one  another,  as  shown,  from  opposite 
sides.  Two  bent  glass  tubes  fused  on  the  outside  of  the  bulb,  are  de- 
signed to  receive  the  mercury  into  which  protrude  the  platinum  wires 
passing  through  the  sides  of  the  glass.  It  will  be  evident  that  we 
can,  without  danger  of  breaking  off  any  platinum  terminals,  make 
and  break  electrical  connection  as  often  as  we  see  fit  by  simply 
immersing  our  conductors  in  the  tubes  and  allowing  them  to  dip  into 
the  mercury.  Another  design  of  cell  for  conductivity  determination 
is  shown  in  Fig.  123  where  we  have  a  special  U-shape  design  of 
tube  with  platinum  disks,  horizontally  hung  from  platinum  wires 

259 


260 


EXPERIMENTAL   ELECTROCHEMISTRY. 


sealed  into  the  bottoms  of  glass  tubes,  which  in  turn  are  supported 
by  turned  wooden  stoppers.  These  tubes  also  receive  a  small 
quantity  of  metallic  mercury,  by  means  of  which  contact  is  made 
with  the  electric  battery  or  other  source  of  current. 

Fig.  124  shows  still  another  form  of  cell  for  conductivity  deter- 


1 


H 


V 


J 


FIG.  123. 


\ 

FlG.   122. 


FIG.  124. 


minations,  and  has  the  advantage  of  allowing  for  temperature  deter 
mination  being  made  at  both  anode  and  cathode.     For  this  purpos 
it  is  only  necessary  to  remove   the    glass    stoppers  and  insert  the 
thermometers.     Such   a   conductivity   cell  may   be  separated   into 
two  useful    parts   by  cutting    through    the    glass   connecting  ned 
with  a  sharp  file  and    joining  them  at  almost  any  distance  from 
one  another  by  inserting  a  glass  tube  and  rubber  connectors.      W 
will   then  have  a  piece  of  apparatus   enabling  us  to  obtain   anod 


USEFUL   PIECES   OF   APPARATUS. 


261 


and  cathode  temperatures,  to  measure  absolute  velocity  of  the  ions, 
etc.,  etc. 

Fig.  125  shows  a  conductivity  cell  for  very  accurate  determina- 
tions, as  we  have  here  means  not  only  for  making  a  careful  tempera- 
ture observation  and  correction,  for  keeping  the  temperature  constant 
by  immersing  the  cell  within  a  calorimeter  receptical,  or  glass  cylin- 
der, which  may  be  packed  with  ice. 


FIG.  125. 


FIG.  126. 


Fig.  126  illustrates  still  another  type  of  conductivity  cell,  which 
consists  of  a  cylindrical  glass  vessel  containing  two  large  platinum 
disks  fitted  loosely  within  the  interior  and  supported  respectively 
by  two  glass  tubes,  through  which  platinum  stems  are  fused.  These 
tubes,  like  those  in  the  previous  chapter,  are  designed  to  be  filled, 
or  partly  filled,  with  mercury  for  the  purpose  of  electrical  contact, 
and  the  turned  wooden  top  with  holes  to  receive  these  tubes  with  a 
tight  fit  completes  the  equipment.  The  center  tube  carries  an  ordi- 
nary disk,  as  shown,  suspended  by  a  platinum  stem  from  its  center, 
but  the  tube  on  the  right  has  its  disk  suspended  from  a  point  eccentric, 


262 


EXPERIMENTAL   ELECTROCHEMISTRY. 


the  center  of  the  disk  being  punched  out  to  allow  the  middle  glass 
tube  carrying  the  lower  disk  to  pass  through.  By  means  of  such  an 
arrangement  the  disks  may  be  brought  near  together  or  separated, 
and  apart  from  serving  the  purpose  of  a  useful  conductivity  cell, 
may  be  employed  also  as  a  very  handy  and  desirable  electrolytic 
rheostat  for  delicate  work.  Every  electrolytic  laboratory  should 
be  equipped  with  a  variety  of  ready  decomposition  tubes  of  various 
shapes  and  patterns,  to  be  to  the  electrochemist  what  the  ordinary 
test-tube  is  to  the  general  chemist. 

Fig.  127   illustrates  a  simple  type  of  "electrolytic  test-tube"  of 


FIG.  127. 


FIG.  128. 


V  shape,  equipped  with  platinum  electrodes.  Test-tubes  of  this  pat- 
tern are  exceedingly  useful  when  made  from  glass,  only  a  few  milli- 
meters in  diameter  and  2  or  3  centimeters  in  height.  There  should 
also  be  test  tubes  of  this  type  several  centimeters  in  diameter  and  15 
or  20  centimeters  in  height,  for  the  tube  is  of  such  general  utility 
that  it  should  be  at  hand  in  several  sizes. 

Fig.  128  is  a  useful  design  of  cell  not  only  for  collecting  gases 
liberated  at  the  electrodes,  but  also  for  solids  which  become  detached 
and  fall  to  the  bottom.  It  consists  merely  of  a  U  tube  equipped 
with  electrodes,  and  a  glass  bulb  blown  upon  the  lower  extremity. 


USEFUL  PIECES   OF  APPARATUS. 


263 


Such  a  U  tube  equipped  with  a  bulb  serves  a  useful  experimental  pur- 
pose when  employed  in  the  electrolysis  of  chloride  of  zinc  where  it  is 
present  in  a  concentrated  aqueous  solution.  When  this  is  connected 
with  our  lamp-bank  and  the  current  allowed  to  flow  for  a  sufficiently 
long  time,  the  bulb  will  be  filled  with  beautiful  crystals  of  metallic 
zinc,  whereas,  if  we  use  a  small  U  tube  the  branch-like  growth  would, 
instead  of  breaking  off  and  falling  into  the  bulb,  extend  across  to 
the  positive  electrode  and  short-circuit  the  cell.  It  will,  therefore, 
be  seen  that  such  a  U  tube  with  bulb  serves  as  a  receptical  for 
certain  electrode  products,  and  therefore  fills  a  useful  purpose. 
The  U  tube,  as  depicted  in  Fig.  129,  is  of  special  construction 


FIG.  129. 


and  is  designed  to  allow  a  removable  porous  partition  to  be  placed 
between  the  electrodes.  This  partition  or  diaphragm  may  be  of 
filter-paper,  parchment,  or  even  a  disk  of  baked  porous  material, 
as  the  requirements  may  dictate.  The  lower  ends  of  the  U  tube 
terminate  in  a  bell-shape  mouth,  over  which  a  clamp  may  be  fixed 
to  draw  them  into  close  contact  with  the  separating  membrane. 
Such  a  piece  of  apparatus  will  serve  only  in  special  cases,  but  it  has 
its  application  in  research  work  and  should  be  included  in  an  equip- 
ment. 

Fig.  130  illustrates  the  front  and  side  view  of  a  Hoffmann  appara- 
tus, blown  from  one  piece  of  glass,  which  deserves  a  special  place  of 


264 


EXPERIMENTAL   ELECTROCHEMISTRY. 


honor  as  a  device  of  general  utility.  Although  small  pieces  of 
Hoffmann  apparatus  may  be  ordered  from  almost  any  dealer  in 
chemical  ware,  when  necessary  to  employ  such  a  cell  on  a  large 
scale,  it  will  be  convenient  and  easy  to  improvise  one  by  using  a  long 
length  of  glass  combustion  tubing  of  large  bore.  If  a  Woulf's  bottle 
with  three  wide  necks  is  available,  the  assembling  of  a  large  Hoff- 


r 
p 

•*• 

v_ 

_L= 

1 

A 

Q 

•iWH 

FIG.  130. 


mann  apparatus  is  a  comparatively  simple  matter,  as  will  be  seen 
by  any  one  with  aptitude  for  construction.  In  place  of  the  Woulf 
bottle  a  large  Hoffmann  apparatus  for  the  accumulation  of  large 
quantities  of  electrode  gas  may  be  assembled  from  the  combustion 
tubing  and  a  large  T  joint  of  glass  with  rubber  connectors. 

In  closing  this  chapter  a  few  words  relative  to  the  Wenhelt  inter- 
rupter and  aluminum  rectifier  will  perhaps  be  of  interest  and  value 
to  us.  Wenhelt's  electrolytic  interrupter  is  particularly  useful 


USEFUL  PIECES  OF  APPARATUS. 


265 


in  connection  with  the  operation  of  induction-coils,  for  it  serves 
to  take  the  place  of  the  ordinary  vibrator. 

Fig.  131  shows  a  simple  form  of  electrolytic  interrupter,  which 
consists  simply  of  a  beaker  glass  containing  dilute  sulphuric  acid, 
into  which  is  immersed  strips  of  platinum  to  serve 
as  anode,  while  the  cathode  consists  of  a  short 
piece  of  platinum  wire  fused  into  the  lower  end 
of  a  stout  glass  tube,  bent  as  shown  in  the  illustra- 
tion. This  tube  is  filled  with  mercury,  both  for 
the  purpose  of  making  an  electrical  contact  with 
the  platinum  wire  cathode  and  for  conducting 
away  the  heat  which  is  generated  there.  When 
interposed  in  an  electrical  circuit  this  device 
serves  to  rapidly  make  and  break  the  electric  cur-  FIG.  131. 

rent.  The  principle  of  this  interrupter  is  based 
upon  the  rapid  formation  and  discharge  of  bubbles  of  hydrogen  from 
the  platinum  point  or  cathode  of  the  cell  which,  because  of  the  high 
current  density  existing,  becomes  quite  hot.  Such  an  interrupter 
operates  in  a  most  satisfactory  manner  an  induction-coil  and  other 
devices  where  an  intermittent  current  is  desired.  The  adjustment 
is  brought  about  by  varying  the  distance  between  the  platinum  strip 
anode  and  the  platinum  cathode,  together  with  changing  the  concen- 
tration of  the  sulphuric  acid  solution.  This  apparatus  is  introduced 
here  as  of  scientific  interest  from  an  electrochemical  standpoint,  in  the 
belief  that  the  student  will  profit  by  conducting  experiments  there- 
with. Another  electrolytic  cell  of  remarkable  performance  is  the 
aluminum  rectifier,  which,  when  placed  in  series  in  the  circuit  of 
an  alternating  current,  converts  the  alternating  current  into  an  inter- 
mittent direct  current.  This  may  be  regarded  as  a  species  of  elec- 
trical "check- valve,"  allowing  the  impulses  in  one  direction  to  pass 
through  and  preventing  the  impulses  in  the  opposite  direction  from 
getting  past.  Such  a  rectifier  consists  simply  of  a  beaker  glass  con- 
taining a  suitable  electrolyte,  into  which  is  immersed  an  aluminum 
anode  and  a  platinum  cathode.  With  such  an  equipment,  using 
disodium  phosphate  as  an  electrolyte,  a  potential  difference  as  high 
as  300  volts  may  be  established  between  the  electrodes,  while  only 
a  few  hundredths  of  an  ampere  will  flow  through  the  cell  in  one 
direction,  because  of  its  high  resistance,  whereas  the  resistance  is 


266  EXPERIMENTAL   ELECTROCHEMISTRY. 

comparatively  zero  in  the  reverse  direction.  Such  a  cell  interposed 
in  an  alternating  current  circuit  with  only  no  volts  pressure  is  of 
exceedingly  great  interest.  It  is  necessary  to  keep  these  cells  cool 
by  the  circulation  of  water,  and  for  this  purpose  the  aluminum  elec- 
trode has  been  employed  in  the  form  of  a  U  tube,  through  which  cold 
water  may  be  made  to  flow.  The  principle  of  the  rectifier  is  believed 
to  be  based  upon  the  formation  of  a  non-conducting  film  upon  the 
aluminum,  and  which  allows  a  large  current  to  pass  through  in  one 
direction,  but  only  an  exceedingly  small  one  in  the  other. 


CHAPTER   XX. 
BIBLIOGRAPHY,     CHRONO  GRAPHIC  ALLY  ARRANGED. 

Galvani,  L.     "De  Viribus  electricitatis  in  motu  muscular!."     Bologna,  1791. 

(With  Aldini's  commentary,  Modena,  1792.) 
Fowler,  R.     "  Experiments  and  Observations  relative  to  the  influence  lately 

discovered  by  M.  Galvani."     Edinburgh,  1793. 
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Paris,  1799. 
Volta,  A.     "  Rapport  fait  k  PInstitut  National  sur  les  experiences  du  citoyen 

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Ritter,  J.  W.  "Beitrage  zu  nahern  Kentniss  des  galvanismus."  Jena,  1800. 
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Litter.)     1802. 

Sue,  P.     "Histoire  du  Galvanisme."     Paris,  1802. 
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Carpue,  J.  C.     "An  Introduction  to  Electricity  and  Galvanism."     London,  1803. 
Dal  Negro,  S.     "Del  elettricismo  idri-metallico."     Padua,  1903. 
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Izarn,  J.     "Manuel  du  galvanisme."     Paris,  1804. 

Cuthbertson,  J.     "Practical  Electricity  and  Galvanism."     London,  1807. 
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Verona,  1816. 

267 


268  EXPERIMENTAL   ELECTROCHEMISTRY. 

Bostock,  J.     "The  History  and  Present  State  of  Galvanism."     London,  1818. 

Hare,  R.     "A  New  Theory  of  Galvanism."     Philadelphia,  1819. 

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Gumming,  J.  "On  the  Connection  of  Galvanism  and  Magnetism."  Cam- 
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Pohl,  G.  F.     "Der  Process  der  galvanischen  Kette."     Leipsic,  1826. 

Farrar,  J.  "Elements  of  Electricity,  Magnetism,  and  Electro-Magnetism.'' 
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Ohm,  G.  S.  "Die  galvanische  Kette  mathematische  bearbeitet."  (Translated 
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De  La  Rive,  A.  "Recherches  sur  la  cause  de  Pelectricite  voltaique."  Geneva, 
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Anonymous.  "Galvanism  published  under  superintendence  of  the  Society  for 
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Faraday,  M.     "Chemical  Manipulations."     New  edition,  1830. 

Fischer,  N.  W.  "Das  Verhaltniss  der  chemischen  Verwandschaft  galvanisch 
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Fechner,  G.     "Uber  die  galvanische  Kette."     Leipsic,  1831. 

Roget,  P.  M.     "Treatise  on  Galvanism."     London,  1832. 

Ritchie,  W.     "Exp.  Researches  in  Voltaic  Electricity."     London,  1832. 

Becquerel,  A.  C.  "Traite  experimental  de  Pelectricite  et  du  magnetisme." 
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Houwink,  J.     "De  theoria  elementi  apparatus  voltaici."     Groningen,   1835. 

Wartmann,  E.  F.  "Essai  historique  sur  les  phenomenes  et  les  doctrines  de 
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Faraday,  Michael,  D.C.L.,  F.R.S.  "Experimental  Researches  in  Electricity." 
(Page  127.  Electrochemistry.)  Richard  and  John  Edward  Taylor,  Printers 
and  Publishers  to  the  University  of  London,  Red  Lion  Court,  Fleece  St., 
1839. 

Daniell,  John  Frederic.  "Fifth  letter  on  voltaic  combinations,  with  some 
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Hare,  R.  "A  Brief  Exposition  of  the  Science  of  Mechanical  Electricity." 
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Henrici,  F.  C.  "Uber  die  Elektricitat  der  galvanischen  Kette."  Gottengen, 
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BIBLIOGRAPHY,  CHRONOGRAPHICALLY   ARRANGED.         269 

Geruches  welcher  sich  sowohl  aus  positiven  Pole  einer  Saul  Wahrend  die 
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Gore,  G.     "Theory  and  Practice  of  Electro-deposition."     London,  1856. 
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270  EXPERIMENTAL   ELECTROCHEMISTRY. 

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274  EXPERIMENTAL   ELECTROCHEMISTRY. 

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INDEX. 


Accumulator,  237 
Acetylene,  synthesis  of,  211 
Acids,  ionization  of,  II 
Acids,  sulphuric,  electrolysis  of,  108 
Acids,  nitric,  preparation  of  from  atmos- 
phere, 150 

Acids  and  bases,  neutralization  of,  36 
Acids  and  carbonates,  inactive  when  dry, 

43 

Affinity,  chemical,  49 
Agassiz,  95 

Alcohol  as  dissociant,  43 
Alternating  currents,  rectification  of,  265 
Alternating  currents  and  electrolytes,  63 
Aluminum,  isolation  of,  174 
Aluminum  bronze,  184 
Aluminum  rectifier,  265 
Ampere  hour  meter,  89 
Andrews,  140 
Anode,  9 

Anode,  definition  of,  16 
Anode,  rotating,  112 
Apparatus,  useful,  259 
Arc,  temperature  of,  265 
Arrhenius,  5,  17 

Artificial  carnalite,  preparation  of,  105 
Atomic  heat,  table  of,  87 
Attraction,  chemical,  10 
Avogadro's  law,  20 
Ayrton,  243 
Azobenzene,  216 

Bases,  neutralization  of,  36 

Battery,  chemistry 'and  electrochemistry 

of  Daniell's,  234 

Battery,  chemistry  of  storage,  243 
Battery,  density  changes  in  storage,  242 
Battery,  depolarization  in,  238 
Battery,  discharge  curve  of  storage,  241 
Battery,  polarization  m,  237 
Battery,  primary,  theory  of,  219 
Battery,  secondary,  theory  of,'  237 
Battery;  thermo-electric,  2$2 
Bauxite,  174 
Becaria,  I 


Beckmann's  thermometer,  33 
Becquerel,  140,  254 
Berthelot,  212 
Bertoli,  257 
Berzilius,  3 
Bibliography,  267 
Bladder,  experiment  with,  22 
Bloxam,  145 

Boiling-point,  elevation  of,  34 
Boiling-point,  influence  by  electrolytes,  34 
Boiling-point,   influence   by   non-electro- 
lytes, 34 

Borscher,  168,  170,  177,  191 
Boyle,  20 
Boyle's  law,  20 
Bradley,  158 
Bredig,  75 
Brugnatelli,  4 

Buckling  in  storage-batteries,  246 
Bumping,  how  to  prevent,  36 
Bunsen,  177,  187 

Cadmium  yellow,  126 

Calcium,  isolation  of,  186 

Calcium  carbide,  preparation  of,  205 

Calorie,  49,  102 

Calorimeter  for  measuring  neutralization 

heats,  37 
Carbide,  205 

Carbon,  electricity  from,  250 
Carbon,  ionization  of,  257 
Carbon,  solution  of,  257 
Carbon  disulphide,  preparation  of,  213 
Carlisle,  3 

Carnalite,  preparation  of  artificial,  105 
Castner,  166 
Cathode,  9 

Cathode,  definition  of,  16 
Caustic  soda  and  chlorine  from  salt.  121' 
Cavendish,  151 
Cells,  conductivity,  159 
'  Ctiemical  action  at  a  distance,"  224 
Chemically  active  bodies,  18  { 

Chemical  activity  and  dissociation,  18 
Chemical  affinity,  49 

2/cr 


280 


INDEX. 


Chemical  attraction,  10 
Chemical  equivalents,  83 
Chemically  inactive  bodies,  18 
Chemical     indicator,     reflecting     galva- 
nometer as,  63 
Chloride  of  lime,  12 1 
Chloroform,  electrolytic    preparation  of, 

211 

Chronograph,  diagram  of  connections  of 
Hopkins.  69 

Chronograph,  use  in  studying  electro- 
lytes, 68 

Coehn,  257 

Collins,  8 1 

Conduction,  electrodeless,  61 

Conductivity,  molecular,  49 

Conductivity  cell,  259 

Conductivity  and  dissociation,  46 

Conductors,  first  class,  17 

Conductors,  first  and  second  class  com- 
pared, 68 

Conductors,  second  class,  17 

Conservation  of  energy,  101 

Converter,  rotary,  16 

Copper  ferrocyanide,  use  for  semi-per- 
meable membranes,  23 

Coulomb,  92 

Coulombmeter.     See  Voltameter. 

Crookes,  Sir  William,  153 

Cruikshank,  3 

Cryolite,  174 

Current,  direction  of,  II 

Current  density,  117 

Current  indicator,  12 

Daniell  cell,  chemistry  and  electrochem- 
istry of,  235 

Daniell  cell,  electromotive  force  of,  236 
'Davy,  Sir  Humphry,  4,  166 
De  la  Rive,  140,  220 
Depolarization  in  primary  batteries,  238 
Deville,  175,  177 
Diaphragm,  semi-permeable,  22 
Diffusion,  22 

Dissociation  and  chemical  activity,  18 
Dissociation  and  conductivity,  46 
Dissociation  theory  and  the  primary  cell, 

222 

Dissociant,  43,  49 
Dissociants,  table  of,  45 
Distilled  water  as  conductor,  18 
Double  layer,  Helmholtz's,  229 
Dulong,  87 
Dye,  yellow,  preparation  of,  215 

Edison,  258 

Elbs,  136 

Electric  furnace,  194 

Electric  furnace,  Hopkin's  "series  car- 
bon," 2OI 

Electric-lighting  current,  how  to  adapt 
for  electrolytic  work,  14 


Electrical  energy,  correlation  of,  253 

Electricity  from  carbon,  250 

Electricity,  thermo,  252 

Electrochemical  equivalent,  8 1 

Electrochemical  equivalents,  table  of,  84 

Electrochemical  equivalent  of  electricity, 
82 

Electrochemical  order  of  elements,  10 

Electrode,  definition  of,  16 

Electrode,  normal,  230 

Electrode,  negative,  9 

Electrode,  positive,  9 

Electrode  area,  influence  of.  See  Cur- 
rent Density. 

Electrode  tension  in  separation  of  metals, 
in 

Electrodeless  conduction,  Hopkins'  ex- 
periment to  show,  61 

Electrolysis,  conditions  governing  success 
in,  117 

Electrolysis,  definition  of,  16 

Electrolysis,  energy  absorbed  in,  92,  100 

Electrolytes,  n 

Electrolytes,  definition  of,  16 

Electrolytes,  alternating  currents  with, 
change  of  frequency,  63 

Electrolytes,  frozen,  94 

Electrolytes,  fused,  102 

Electrolytes,  law  of  conductivity,  75 

Electrolytes,  lowering  of  freezing-point 
by,  3 2 

Electrolytes,  table  of,  18 

Electrolytes,  Wheatstone's  bridge  ap- 
plied to,  73 

Electrolytes  and  alternating  currents,  63 

Electrolytes  and  non-electrolytes,  table 
of,  18 

Electrolytic  conductivity,  definition  of,  16 

Electrolytic  dissociation,  definition  of,  16 

Electrolytic  dissociation,  evidence  for,  17 

Electrolytic  dissociation,  experiment  in 
support  of,  40 

Electrolytic  dissociation  and  gas  laws,  20 

Electrolytic  dissociation  and  heat  neu- 
tralization, 38 

Electrolytic  induction,  50 

Electrolytic  induction,  effect  on  magnetic 
needle,  59 

Electrolytic  oxidation,  215 

Electrolytic  reduction,  216 

Electrolytic  separation  of  metals,  no 

Electro-magnetic  deportment  of  sub- 
stances in  solution,  50 

Electromotive  force  of  Daniell  cell,  236 

Electromo.ive  force,  electrolysis,  mini- 
mum required  in,  103 

Electromotive  force,  method  of  calculating 
in  primary  cells,  235 

Electromotive  force  and  solution  tension, 
223 

Electrostatic  deportment  of  substances  in, 
solution,  50. 


INDEX. 


281 


Elements,  electrochemical  order  of,  10 

Elements,  negative,  10 

Elements,  positive,  10 

Energy  absorbed  in  electrolysis,  92,  loo 

Energy,  conservation  of,  101 

Energy,  correlation  of,  253 

Energy,  electrical,  correlation  of,  253 

Energy,  heat,  correlation  of,  253 

Energy,  mechanical,  correlation,  253 

Ethane,  production  of.  209 

Ethyl  alcohol  as  dissociant,  45 

Experiment,  absolute  velocity  of  ions, 
Whetham's,  78 

Experiment,  absolute  velocity  of  hydro- 
gen ions,  Lodge's,  76 

Experiment,  alternating  currents  at  differ- 
ent frequencies,  Hopkins',  64 

Experiment,  bladder  to  show  osmosis,  22 

Experiment,  chronograph  in  electrolytic 
conduction,  Hopkins',  68 

Experiment,  Davy's  classic,  Sir  Hum- 
phry,  4 

Experiment,  with  dry  gases,  41 

Experiment,  electrical  conduction,  in- 
stantaneous, 67 

Experiment,  electrode  less  conduction, 
Hopkins',  62 

Experiment,  electrolysis  of  magnesium 
chloride,  104 

Experiment,  electrolysis  sodium  hydrox- 
ide, 9 

Experiment,  electrolytes  effect  on  mag- 
net, Hopkins',  56 

Experiment,  electrolytes  frozen,  Hop- 
kins', 95 

Experiment,  electrolytes,  magnetic  pull 
of,  Hopkins',  61 

Experiment,  electrolytes,  quantitative 
effect  of  magnet  on,  Hopkins',  58 

Experiment,  electrolytes  from  non-elec- 
trolytes, to  distinguish,  19 

Experiment,  electrolytic  conduction,  effect 
on  magnetic  needle,  Hopkins',  59 

Experiment,  electrolytic  dissociation,  47 

Experiment,  Faraday's  law,  to  demon- 
strate, 84 

Experiment,  free  ions,  Ostwald's,  51,  54 

Experiment,  free  ions,  Hopkins',  54 

Experiment,  glass  as  a  conductor,  Hop- 
kins', 94 

Experiment,  heat  convection  in  electro- 
lytic conduction,  Hopkins',  97 

Experiment,  matter,  mechanical  tran- 
sport of,  93 

Experiment,  nitric  acid  from  atmosphere, 
160 

Experiment,  sulphuric  acid,  electrolysis 
of,  Hopkins',  108 

Fabroni,  2 

Faraday,  Michael,  52,  80,  220 

Faraday's  law,  80 


Faraday's  law,  experimental  demonstra- 
tion of,  84 

Faraday's  law  and  primary  cell,  234 
Feldspar,  174 

Formic  acid  as  dissociant,  45 
Freezing-point,  depression  of,  32 
Freezing-point,    practical    determination 

of,  35 

Fremy,  140 

Frequency,  in  alternating  currents  ap- 
plied to  electrolytes,  63 

Froelich,  142 

Frozen  electrolytes,  94 

Furnace,  electric,  194 

Furnace,  electric,  Hopkins'  series  car- 
bon, 201 

Fused  electrolytes,  102 

Galvani,  2 

Galvanometer,  reflecting  as  chemical  in- 
dicator, 53 

Gas  laws,  application  to  substances  in 
solution,  20 

Gaugin,  53 

Gay-Lussac's  law,  20 

Geber,  151 

Gerboin,  3 

Gladstone  and  tribe,  247 

Glass,  conductivity  of,  93 

Glauber,  151 

Gore,  221 

Grabau,  175 

Gram-molecular  weight,  31 

Gram -molecule,  48 

Gunpowder  incombustible  when  dry,  43 

Hall,  180 

Heat  of  combustion,  190 

Heat  convection  in  electrolytic  conduc- 
tion, 97 

Heat  energy,  correlation  of,  253 

Heat  of  formation,  100 

Heat  of  formation,  table  of,  102 

Heat  of  formation  of  salts,  39 

Heat  of  formation  of  water,  39 

Heat,  latent,  35,  48 

Heat  of  neutralization,  36 

Heat  of  neutralization  and  electrolytic 
dissociation,  38 

Heimrod,  81 

Helmholtz's  double  layer,  229 

Henry,  Joseph,  3,  250 

Herault,  184 

Hess,  ico 

Kissinger  and  Berzelius,  3 

Hittorf,  114 

Hoffman's  apparatus,  216,  264 

Hopkins'  electric  furnace,  series  carbon, 
201 

Hopkins'  electrolysis  of  sulphuric  acid, 
107 


282 


INDEX. 


Hopkins'  electrode  temperatures,  method 
for  studying,  119 

Hopkins'  experiment  to  show  dissociation 
simultaneously  in  two  ways,  47 

Hopkins'  experiment  to  show  electrode- 
less  conduction,  62 

Hopkins'  experiment  to  show  electrolytic 
induction  upon  magnetic  needle,  59 

Hopkins'  experiment  in  heat  convection 
in  electrolytic  conduction,  97 

Hopkins'  experiment  to  show  velocity  of 
electrolytic  conduction,  68 

Hopkins'  experiment  to  show  deportment 
of  electrolytes  with  alternating  currents 
at  various  frequencies,  64 

Hopkins'  experiment  with  frozen  electro- 
lytes, 94 

Hopkins'  experiment  to  show  effect  of 
magnet  upon  coil  of  electrolyte,  56 

Hopkins'  experiment  to  show  magnetic 
effects  upon  electrolytes,  58 

Hopkins'  experiment  to  show  and  meas- 
ure pull  of  coiled  electrolyte,  61 

Hopkins'  experiment  with  glass  as  con- 
ductor,  93 

Hopkins'  experiment  in  magnetic  induc- 
tion, 56 

Hopkins'  experiment  in  static  induction 
to  show  free  ions,  54 

Hopkins'  high  speed  chronograph,  68 

Hopkins'  reflecting  hydrometer,  242 

Hopkins'  Soret  apparatus,  design  of,  29 

Hopkins'  table  of  electrochemical  condi- 
tions to  be  noted,  120 

Houzan,  145 

Howies,  153 

Hydrogen,  occlusion  in  storage-batteries, 
240 

Hydrogen  ion,  absolute  velocity  of,  77 

Hydrometer,  reflecting,  Hopkins,  242 

Hysterisis  of  iron,  63 

Indicator,  reflecting  galvanometer  as 
chemical,  53 

Interrupter,  Wenhelt's,  264 

lodoform,  electrolytic  preparation  of,  209 

Ions,  8 

Ions  complex,  II 

•Ions,  conduction  through  an  electrolyte, 
instantaneous,  due  to,  67 

Ions,  definition  of.  16 

Ions,    existence   shown   by   experiments, 

T  50,  56 

Ions,  heat,  transported  by,  97 

Ions,  hydrogen,  absolute  velocity  of,  77 

Ions,  inertia  of,  65 

Ions,  mechanical  representation  of  migrat- 
ing, Hopkins,  60 

Jons,  negative,  10 

Ions,  positive,  10 

Ions,  presence  of  free  ions  shown  by 
chronograph  work,  Hopkins,  68 


Ions,  simple,  II 

Ions,  velocity  of,  absolute,  76,  97 

Ions,  velocity  of,  relative,  114 

Ions,    velocity,    Whetham's    method    for 

determining,  78 

lonization  of  acids,  hydrochloric,  n 
lonization  of  acids,  nitric,  II 
lonization  of  acids,  sulphuric,  u,  108 
lonization  of  carbon,  257 
Isolation  of  aluminum,  174 
Isolation  of  calcium,  186 
Isolation  of  magnesium,  104 
Isolation  of  sodium  and  potassium,  165 

Jablochkoff,  254 
Jacques,  255 
Jahn,  209 
Joule,  92,  102 

Kahle,  81 

Kanarin,  electrolytic  preparation  of,  215 

Kaolin,  174 

Kohlrausch,  73,  81 

Kowalski,  158 

Kuester,  54 

Lamp-bank,  application   to  lighting  cir- 
cuit, 13 

Latent  heat,  35,  48 
Laws,  Avogadro's,  20 
Laws,  Boyle's,  20 
Laws,  Dulong  and  Petit,  87 
Laws,  Faraday's,  80 
Laws,  Gay-Lussac's,  20 
Laws,  Hess's,  100 
Laws,  Ohm's,  14 
Lead,  white,   electrolytic  preparation  of, 

122 

Le  Blanc,  in 

Litmus  paper  unaffected  by  dry  acids  and 

bases,  43 
Lodge,  76 
Lodge's  method  for  determining  absolute 

velocity  of  hydrogen  ion,  77 
Love  joy,  158 
Lullius,  151 

McDougall,  153 

Magnesium  chloride,  electrolysis  of,  104 

Magnetic  needle  affected  by  electrolytic 

induction,  59 
Marignac,  140 
Matthiessen,  187 

Mechanical  energy,  correlation  of,  253 
Membranes,  semipermeable,  22 
Membranes,    semipermeable,    method    of 

preparing,  24 

Methyl  alcohol  as  clissociant,  45 
Mercury  as  pole  finder,  12 
Mercury  vermillion,  128 
Metals,  electrolytic  separation  of,  1 10 
Metals,  table  of  tension  series,  234 


INDEX. 


283 


Metals  and  their  salts,  potentials  between, 

233 

Meter,  ampere  hour,  89 

Meter,  calorimeter,  89 

Meter,  coulombmeter,  88 

Meter,  gas-type  voltameter,  88 

Meter,  voltameter,  105 

Mica,   174 

Moisture,  influence  in  reactions,  43 

Molecular  conductivity,  49 

Molugram,  45,  48 

Moscicki,  158 

Motor-generator,  15 

Motor-generator,  diagram  showing  appli- 
cation, 15 

Nernst,  Walter,  52,  87,  229 

Neumann,  233 

Neutralization  of  acids  and  bases,  36 

Neutralization  heats,  calorimeter  for  de- 
termining, 37 

Newton,  153 

Nicholson  and  Carlisle,  3 

Nitric  acid,  ionization  of,  II 

Nitric  acid,  production  of  from  atmos- 
phere, 150 

Nitrobenzene,  electrolysis  of,  216 

Non-electrolytes,  freezing-point  lowered 
by,  32 

Non- electrolytes,  table  of,  18 

Normal  electrode,  230 

Normal  solution,  sugar,  27 

Occlusion  of  hydrogen  in  secondary  bat- 
teries, 240 

Oersted,  175 

Ohm's  law,  14 

Organic  compounds,  preparation  of,  207 

Osmotic  pressure,  21 

Osmotic  pressure,  experiment  with  blad- 
der, 22 

Osmotic  pressure,  theory  of,  26 

Ostwald,  Wilhelm,  50,  66,  87,  224,  256 

Ostwald's  experiment  to  show  existence 
of  free  ions,  50 

Ostwald's  and  Nernst' s  experiment  to  show 
existence  of  free  ions,  53 

Oxidation,  118 

Oxidation,  electrolytic,  215 

Oxidation  and  reduction,  118 

Oxygen  non-supporter  of  combustion  in 
moisture  free  substances,  43 

Ozone,  139 

Ozone,  commercial  production  of,  146 

Ozone,  experimental  production  of,  139 

Paetz  and  Van  Troostvik,  I 
Papasogli  and  Bertoli,  257 
Passive  state,  8 
Patterson,  81 
Pellat,  81 
Petit,  87 


Pfeffer,  23 

Phenolphthalein  as  a  chemical  indicator, 

46 

Plante,  244 
Polarization,  in 
Polarization  in  batteries,  237 
Polarization  currents,  ill 
Pole  finder,  electrolytic,  9 
Porous  pots,  use  in  preparing    semiper- 

meable  membranes,  23 
Portier,  81 

Potassium,  isolation  of,  165 
Potassium  chlorate,  133 
Potentials  between  metals  and  their  salts, 

233 

Power,  primary,  250 
Primary  cell,  219 
Primary  cell,  theory  of,  226 
Primary  cell  and  Faraday's  law,  234 
Prime  movers,  250 
Principle  of  Soret,  28 
Prussian  blue,  131 

Ramsay,  158 

Rauolt,  32 

Rayleigh,  Lord,  81,  153 

Reactions,  chemical,  moisture   influence 

in,  43 

Rectification  of  alternating  currents,  265 
Rectifier,  aluminum,  265 
Reduction,  118 
Reduction,  electrolytic,  216 
Reflecting    galvanometer   as  a   chemical 

indicator,  54 

Reflecting  hydrometer,  Hopkins,  242 
Resistance,  lamp-bank  as,  13 
Rheostat,  useful,  262- 
Richards,  81 
Rose,  175 

Rotary -converter,  16 
Rotating  anode,  112 

Salts,  table  showing  heat  of  formation,  39 

Scheele's  green,  preparation  of,  130 

Schoenbein,  139 

Secondary  cell,  237 

Secondary  cell.     See  Storage  battery 

Sedgewick,  Mrs.,  81 

Seeback,  252 

Sellon,  243 

Semipermeable  membrane,  22 

Semipermeable     membrane,    method     of 

preparing,  24 
Semipermeable  membranes,  use  of  porous 

pots  in  preparing,  23 
Siemen's  tubes,  142 

Silver,  electrochemical  equivalent  of,  8 1 
Sodium,  isolation  of.  165 
Sodium  acetate,  electrolysis  of,  207 
Sodium  hydroxide,  electrolysis,  minimum 

voltage  for,  172 
Solution  tension  of  metals,  222 


284 


INDEX. 


Solution  tension  and  electromotive  force, 

223 

Soret,  28,  140 
Soret,  principle  of,  28 
Specific  heat,  49 
Specific  inductive  capacity,  49 
Steam-engine,  non-efficiency  of,  25 1 
Storage- battery,  "boiling"  in,  248 
Storage-batteries,  "buckling"  in,  246 
Storage-batteries,  calculation  for  capacity, 

248 

Storage- batteries,  care  in  charging,  247 
Storage-batteries,  chemistry  of,  243 
Storage -batteries,  density  changes  in,  242 
Storage-batteries,  discharge  curve  of,  241 
Storage-batteries,     electromotive     force, 

calculation  of,  248 

Storage-batteries.     See  Secondary  cells 
Sugar,    table    showing  osmotic  pressure 

of,  26 

Sulphur  trioxide,  137 
Sulphuric  acid,  electrolysis  of,  197 
Sulphuric  acid,  ionization  of,  II,  108 
Sulzer,  i 
Synthesis  of  acetylene,  211 

Tait,  140 

Taylor,  214 

Temperature  of  electric  arc,  205 

Tension  series  of  metals,  234 

Tension  solution  of  metals,  222 

Tension,  vapor,  222 


Thermoelectric  current,  252 
Thermostat,  air-bulb,  30 
Thomson,  J.  J.,  43 
Trauve,  Moritz,  23 
Treadwell,  245 
Tyndall,  95 

Van't  Hoff,  27,  30 

Vapor  tension  of  liquids,  222 

Volt-coulomb.     See  Joule 

Volta,  Alexander,  2 

Voltameter,  metal  and  gas  type,  88 

Voltmeter,  105 

Von  Helmholtz,  80 

Von  Marum,  139 

Von  Troostvik,  I 

Wade,  248 
Warburg,  148 
Water  as  conductor,  18 
Water  as  dissociant,  45 
Water,  feeezing- point  lowered,  32 
Water,  heat  of  formation,  39 
Watt,  1 66 

Welhelt's  interrupter,  264 
Wheatstone's  bridge,  application  to  elec- 
trolytes, 73 
Whetham,  78 
Wohler,  175 
Wollaston,  3 

Zosimus,  I 


$ 


